We just launched PayScroll (
http://www.payscroll.com ) and I've been trying out various ads system. Adword, Yahoo Search Marketing, Text-Link-Ads and almost PPP (payperpost). Here's what I have been seeing so far. And bare in mind, this is with a $200 budget.
Adword - Expensive. we are bidding around $0.15 - $0.25 CPC. Clicks comes from search and sites. And also you got charge for impressions. We had to pay $$ for impression from a campaign that brought in zero clicks. Remember, Google is stock is at $600 for a reason. If you have a huge budget and can place high bids, it might work for you.
Yahoo Search Marketing - Slightly less expensive and lower CPC with more click through. We signed up through Yahoo SB account and you get $50 sign up promotional credit but the catch is you have to deposit min $30 so you get $80 to burn. So a plus if you have a small budget. No cost per impression just pure CPC.
Text-link-ads - So far not a whole lot of clicks with $125 worth of links. Total links we bought - 5. Main purpose is increasing your pagerank (wishful thinking?). Promotional $100 so overall we paid $25 out of pocket.
PayPerPost - Pay per post sounds interesting at first. And we submited an opportunity through PPP direct. Basically PPP direct is you make an offer to the blog owner and the blog owner will decide to accept your offer to review your site, etc. We did not go through because the offer was pending for days for some reason. So no deal there.
Again this is what we are at with $200 and might not hold true if you have a huge budget of 4 digits to burn.