There are quite few mobile ad companies around, here is the list of main ones.
Admob is the first and the biggest mobile advertising company. Fill rate is good and has worldwide advert portfolio. Publisher support is slow and communication is very cold and in automated manner. Pays in time. Doe not accept any adult content, even keywords like hot babes are banned. Recently admob & publishers started to exprience few problems! See this and this posts.
Mojiva is slowly gaining pace. Fill rate is not too bad. Support is slow and usually feels like you are not being valued as publisher. Although you eventually get your payment, their payment system is a mess. Does accept mild adult content.
Buzzcity mainly targets Asia-Pacific region. Fill rate is not too bad. Support is ok and you feel like being valued as publisher. They recently started to expand to Europe. Payments always on time. Publisher control panel is not fancy as others and they only provide PHP and HTML Banenr ad codes. If you are using any other technology you have to write your own by reading their API docs. Accepts adult content.
Decktrade mainly targets Americas. Fill rate is quite low. Support is good. Payments are on time. does not accept adult content.
InMobi is one of the newest on the market and used to known as mKhoj. Mainly targets Asia-Pacific region, recently started to expand in to Europe. Support is excellent. Payments always on time and publishers valued. Accepts adult content.
AdModa Fill rate is quite low. Support is good. Payments are on time. Does not accept adult content.
AdultModa Fill rate is ok. Support is good. Payments are on time. Accepts ONLY adult content. It is the only mobile pure adult advertise company i know.
Smaato is mobile ad optimization platform were they do not signup advertisers but uses other ad platforms such as Admob to display adverts on your site and pay you VERY small share (30% at the time of writing this post). Support is bad. You never get reply to any of your questions unless you are a very big publisher with huge hits! Never pays on time. Update 21/07/2010 Please see comment below from Smaato regarding my info about Smaato.
Update 08/08/2011: So I decided to try Smaato and submited top.web.tr to them. To my suprise they've rejected it claiming it has no content but links to other sites. Doesn't Google do the same thing? Then I've noticed another toplist besttop.mobi runing their ads just fine. Besttop have almost same content with top.web.tr the only difference is that they were around longer then top.web.tr.
A word of advice, do not rely on a 3rd party to run your business!
SGM is a mobile adult affiliate network where you send traffic to their adult content with your affiliate id and get paid if people visiting them from your site buys content. Mainly uses Bango to charge for content. Pays on time but don't expect too much. Support is good.
Gogole Adsense Mobile has mobile advertising platform too. They recently bought Admob and it is not yet clear if they are going to merge Admob in to Adsense Mobile or vice versa.
Greystripe is not a classic mobile ad company. Like SGM they provide you with a content site where your visitors can download free ad supported games and you earn money as your visitors click in game adverts. IT is hard to generate income and as a affiliate you don't get too much return from clicks. Support is slow.
AdFonic I have no information about them yet. If you have any experience don't hesitate to comment.
ZestADZ is another small mobile ad company. Fill rate is low. Support is slow. Again I was unable to find anyone got stayed with them more than a month to gather info about payments. That doesn't mean they are bad, I simply haven't got any information.
Reporo is another player on adult advertising. If you have adult oriented mobile site you can ask them to become their publisher. Their system uses same ad serving platform from http://www.openx.org. The main problem with Reporo is that their system is not automated self serving type. You have to email and ask them to become publisher and if your site accepted you wait them to setup your publisher ids. Wait is not long but nevertheless it is a wait. Support is ok and fillrate is quite high.
Amobee (ex ringringmedia) too allows adult mobile sites to their ad network. Registration process is manual. You fill out a form and they come back to you. They didn’t to me after 3 submissions but came back to one of my friend’s. Setup process is painfully slow as almost everything is manual. They create your account and publisher id and send you details via email. Stats panel is very basic and usually doesn't work properly. I have no information about ad income and payment process yet.
iAd is Apple's advertising network for iOs devices. As far as I know you can’t use it on a mobile site but iOs application. It seems registration is manual. If you have any experience don't hesitate to comment.
Disclaimer. Information above does not reflect my own experience but simply collection of experiences form mobile site developers i know and forums I've read over the last couple of months. I have no reference links and your experience could be totally opposite to what it's been said about these companies in this post.