Well, this is clearly an underdeveloped thread. I was hoping to see what forum members had to say before giving myself a shameless plug.

I'll say this though. There are a lot of good ones out there and a lot of bad ones. When choosing though, do yourself a favor and don't choose a company if you don't know any webmasters that can recommend them. Unfortunately there are a lot of shady companies out there that don't give their players or their affiliates the kind of experience they're looking for.
Here's some things my company does and I'd is what I expect out of any company I would work with as an advertiser in this industry:
- Personal Account Manager that can help optimize my traffic
- Live stats feed
- Regular payments through known payment channels
- An in house design and marketing team that regularly comes out with new promotions and banners
- Provides a great player experience, ie good customer support, multiple language interface, easy payout etc. This one is really important, especially if working on rev share.
Its just a short list to get you started. If you have any questions feel free to email me or chat on messenger/icq