1) Nizoral shampoo (1% is fine) alternated with Neutrogena T-Gel (or generic) or some other type of OTC anti-dandruff shampoo like Head and Shoulders. This keeps your hair in good pH balance and from getting inflammed. Dr. Lee @ Minoxidil.com sells 2% Nizoral + Salicylic acid which works great also. This is the first line of defense in hair loss, and is the cheapest route to go. Since the active ingredient in Nizoral helps prevent DHT from forming on the scalp, it helps prevent MPB and in one study was shown to be as effective as minoxidil. 
2) Topical spironolactone applied twice daily to inhibit DHT/androgens on the scalp. The 2% is liquid, and 5% is a cream (but Dr. Lee also makes a 5% liquid, which is easier to apply). Spiro is available by prescription only. There are very few places that sell topical spironolactone online - it is mostly sold an oral version that is meant to be used as a diuretic. So, you will probably have to buy from Dr. Lee. I also recommend his, as his doesn't smell as badly as many of the other versions (which is a problem with many other topical spiros sold online).
3) Topical zinc/B6/Azelaic acid. All of these have been shown in some studies and by users to have some good ability to inhibit hairloss. Although they aren't as strong as the other items listed above in preventing hairloss, they can help. You can make your own shampoo/topical or buy one from Lee or possibly at some drug or speciality stores. I could not find this combination sold in any of the places I looked, or even zinc/b6 or just azelaic acid. However, I'm sure if you were to search Froogle you could probably come up with something.
Dr. Lee doesn't recommend combining zinc or B6 with his products, as he says that they degrade and become useless. He also says that he isn't sure whether a home brew zinc/B6 topical would work because there haven't been any studies on it. Here is what he had to say when asked about the subject.
Troymaclure asked: "hi Dr. Lee, I don't know if you are
aware of the growing interest of a topical being used whereby the
person mixes a solution (say sufficeint to fill a minoxidil bottle)
of 110mg Zinc Sulphate, 60mg vitamin B6 (p-5-p) and 60ml distilled
water...my question is do you have any thoughts on a) how well this
formula would absorb sufficiently to be effective and b) assuming
it does, what are your personal thoughts on just how effective such
a treatment could be....and if i may put one more point to you;
assuming you feel it is worthwhile, do you think it would be viable
to mix some Zinc Sulphate & B6 in with your spiro lotion, in other
words would the mixture remain stable and would it be as effective
as the distilled water version? Thanks Dr. Lee. "
Dr Richard Lee, MD answered: "I have been reading with interest
some of the accounts of patients who have been treating their
MPB using a mixture of topical zinc and vitamin B6.
Unfortunately, I don't know how well either zinc sulphate
or vitamin B6 is absorbed, when they are applied topically.
I have tried to find this information, but have not been
successful in doing so. Zinc and vitamin B6 are usually
taken in oral forms.
There is some rationale in this proposed treatment for MPB.
Very credible articles (e.g. British Journal of Dermatology
(1988) 119, 627-632) have shown that zinc in high
concentrations could completely inhibit 5-alpha reductase
activity and that vitamin B6 potentiated the inhibitory
effect of zinc. The problem is we don't know if topical
zinc has any efficacy in treating MPB. There is no
evidence that oral zinc is beneficial in the treatment
of MPB. In an excellent article (article),
Dr. Dawber of the Oxford Hair Foundation has written
about the medical history and pharmacology of zinc.
He opens his article, "Zinc supplements: a cure for
hair loss? I believe the short answer to whether zinc
is a cure for hair loss - is NO"
Vitamin B6 is a water-soluble vitamin that exists in
three major chemical forms: pyridoxine, pyridoxal,
and pyridoxamine. Your designation of p-5-p is
pyridoxine 5' phosphate, which is the primary
form of vitamin B6's biological activity.
Since I cannot find any information in regards to
the topical absorption of either zinc sulphate or
pyridoxine 5' phosphate, I can't make an educated
guess in regards to "just how effective such a
treatment could be". Sorry.
Richard Lee, M.D. "
However, people are still using this method with success. I searched around for some bulk zinc powder but didn't find anyone who sold it. I guess there isn't much demand for it. Bulk B6 powder is available at BAC though.
4) Minoxidil is basically a lifetime treatment for the condition of MPB. Yes, you have to use it for the rest of your life if you want to keep having the benefits of minoxidil regrowing the hair on your scalp. Once you stop using it, you can expect to lose the hair you regrew within around 4 months, so once you decide to start using it, expect to use it forever. It's not an easy decision, considering the costs, so do your research and take into consideration before you start.
5) Finasteride works by blocking the conversion of testosterone to DHT through the type 2 5-alpha reductase enzyme. It was originally prescribed for treatment for BPH (prostate enlargement) as the drug Proscar in 5mg tablets, but is now prescribed for MPB as Propecia in 1mg tablets. It eliminates approximately 65% of DHT in the body within 24 hours of a 1mg dosage.  There are two types of the 5AR enzyme, type 1 and type 2 and they are found in different parts of the body. The drug dutasteride (Avodart) blocks conversion through both enzymes. You would assume that this would work better than finasteride since it would eliminate all DHT, but this is not the case. DHT is a potent anti-estrogen and eliminating all DHT in the body can cause symptoms of gynecomastia, lack of libido and strength and other unwanted side effects. It seems that finasteride is a better choice since it leaves you with some DHT systematically, while dutasteride leaves you with virtually none. The best choice, however, still seems to be a topical DHT inhibitor that is site specific. Although DHT is a heavily androgenic compound, it is still necessary in the male body for many functions. Blocking it at the problematic sites would obviously better than blocking it entirely. As with minoxidil, finasteride essentially needs to be taken long term for it's effects to continue working since once you discontinue it your DHT levels would rise back to what they were prior to the initial usage of the drug.
6) Plant Sterols: Beta Sitosterol & Saw Palmetto have been shown in some recent studies to be useful in treating androgenic alopecia when taken orally  and applied topically. They have similar functions to the drug finasteride in regards to blocking DHT conversion, as well as working as partial androgen agonist and antagonist in different organs (such as the prostate). Saw palmetto appears to be a good choice for older men to take as it has been show to assist in reducing the symptoms of BPH and increasing urinary flow through various mechanisms. Beta sitosterol is one of the main actives in saw palmetto and can be purchased as an individual supplement. It can also aid in reducing cholesterol in some people, which is what it is mainly sold for. When buying saw palmetto always make sure it's the standardized extract and beta sitosterol should be in a strength of around 300mg per serving.
During a cycle of AAS, if you are prone to MPB, I would recommend using Nizoral shampoo twice a week along with any other OTC dandruff shampoo inbetween along with 5% topical spiro twice daily. If you have heavy shedding or major problems with MPB then you will want to look into the other methods mentioned in this article. Consult Dr. Lee or your dermatologist for more information.
Dr Lee: Which Hair Medications are Best?
Dr. Lee - MPB FAQ
There are also many other hair loss treatments I didn't mention in this article. If you are concerned with or experiencing hair loss of any type, do plenty of research. There are many sites and forums dedicated to the discussion and treatment of male and female hair loss. A doctor, such as a dermatologist, can help you make decisions about treatments for any hair loss you might be experiencing. You can also find plenty of popular hair loss products, at a great discount, including Minoxidil, Revivogen, Folligen and more at OnlyHairLoss.com - I highly recommend it.
1. Pierard-Franchimont C, De Doncker P, Cauwenbergh G, Pierard GE. Ketoconazole shampoo: effect of long-term use in androgenic alopecia. Department of Dermatopathology, University of Liege, Belgium. Dermatology. 1998;196(4):474-7.
3. Prager N, Bickett K, French N, Marcovici G. A randomized, double-blind, placebo-controlled trial to determine the effectiveness of botanically derived inhibitors of 5-alpha-reductase in the treatment of androgenetic alopecia. Clinical Research and Development Network, Aurora, CO, USA. J Altern Complement Med. 2002 Apr;8(2):143-52.