Maybe Adword is the best campaign you can work with but recently i see that Facebook ads is the best cuz you can target the ppl in their geographic easily and really a nice convert traffic.
I have been trying out Clicksor..Not happy at all to be honest...Ads take ages to be approved and customer support is god-awful...I marked a query as Urgent and get a reply after two days..Bid amounts are pretty low - $0.05 to start with, but I am not sure how good their reporting system is since I was charged for 80 clicks for a Clickbank product but CB's analytics only showed close to 14 clicks! :/
This is the email I got back from Clicksor when I wrote to them about their pathetic customer support: "Please understand that we try to answer all types of tickets ASAP. But we only can guarantee our clients replying within 24 hours Monday to Friday since the volume is high. For Weekend tickets, please wait a little more days until we back to work on Monday." That means, if you got wrongly charged a $1000 on your credit card on a Friday, you will have to wait for the support team to get back on lazy monday to tell you a sorry..Good luck.
Adwords (Google), Facebook self serve ads, MyAds (Myspace), Plenty of Fish, MSN Adcenter. These are obviously the big ones. Smaller middle men agencies often take a large cut of ad spend. It is more work, but often more profitable, to contact small sites directly.