It turns my favorite domain name registrar runs (or just entered) a hosting business, and offers a lot of coupons when signing for a hosting plan! By spending $60 (for Developer hosting plan, that costs $20 per month, minimum period is 3 monthes) one gets a coupons for advertising services for $475 ($200 for MS AdCenter, $100 for AdWords, $75 for Yahoo Search Marketing, $100 for CitySearch). One gets 5 domains names for free too, but in case you don't prolong the hosting after initial 3 monthes, your domains need to be transferred to other registrars; depending on registrar, they can charge you for 1 year during transfer; some of them won't though).
The only limitation is that one has to activate all coupons in 15 days period, but that's not a big deal, I think. So one can get $475 of advertising budget by spending only $60 - very nice deal!