Since there have been some questions about supplies in Taiwan, here are my experiences, no guarantees for completeness or correctness:

The first thing to note is that most of the big international brands are not sold at all in Taiwan; don't ask me why, they simply don't get exported there. You will not find Clearasil or Oxy anywhere, no matter which product category. In most cases, it's not worth looking for the brands you know from North America or Europe. Don't waste your time. (I did and regret.)

Benzoyl Peroxide

Available, but not nearly as popular as elsewhere. Drug stores rarely stock any, some of the biggest outlets sometimes do (as has already been said, try Taipei 101). You can get it from pharmacies, although the smaller ones might even have to order it for you. Knowing the Chinese name (guo4-yang3 hua4-ben3 - "oxidized benzene", preferably written in Chinese characters) helps, as does knowing an available brand name. The only foreign brands which I know are definitely available are Panoxyl, Benoxyl and Stri-dex. There are also at least two local brands (or at least I think they are), called Acnie and Aczo, which might be easier to obtain than the foreign products.

Salicylic Acid

Available, popular; Neutrogena spot control seems to have the largest market share although there are cheaper local alternatives. Can be bought in most drug stores. Haven't seen any clearasil-style face wash so far.

Sulfur

Available under local and Japanese brands; the bigger drug stores have it.

Erythromycin

Unlike in most places, this is available prescription-free, at least in its 2% gel-form. The most widely sold brand seems to be Jumelle anti-acne gel. You can get it at the bigger drug stores. It's occasionally behind the counter, but I have seen it on the shelves as well.

Other options

A variety of locally or Japanese-made antibacterial soap gels and foams are advertised as acne remedies, using agents such as Triclosan or Isopropyl Methylphenol; worth a try for milder Acne I guess.

There is also a whole range of remedies from Chinese traditional medicine. Again, definitely worth a try, although you should get some general advice on it if you are not already familiar with the domain of Chinese traditional medicine. It's a world apart from Western medicine.

Moisturizers

You are spoilt for choice. Taiwanese women are obsessed with skin care, and the assortments are accordingly.

That's my experience. No guarantees, it is only intended as a starting point. For corrections and additions simply follow-up, I would be interested to know as well.