Miva.com - Formerly findwhat.com. A quality engine, should be #3 in the repertiore for any good search engine marketer. Conversion/cost ratio for Miva is very high - find the right keyword and you may get a lot for your money. New Pay Per Call feature - Well worth the money for a local advertiser or national advertiser in which sales leads have a long closing cycle.

Enhance Interactive - Similar to Miva.com. Owned by Marchex, the same guys who founded Go2 which later became Overture. Similar quality to Miva, although be careful about which keywords you choose so you don't run out of funds too quickly. They can provide you with A LOT of keyword traffic for a very low cost.

Additional US-based Pay Per Click Search Engines:

Lycos Insite | ePilot | goClick | Search123 | Searchfeed | 7search | Looksmart | Kanoodle

UK Pay Per Click Search Engines:

espotting | mirago | turbo10 | splut