The thing is, they don't send me much traffic, but the traffic they do send is very targeted and most importantly - free.

See, I don't give them any money, so if it takes a month for them to send me a visitor then that's fine with me. The trick is to be listed at a bunch of them so you get more than 1 click a month. I list with the ones that will fill my account with money from their pocket - Many of them will give you at least $10 to open an account - and when bidding a penny or two, that will last you for a long time.

Now, if the $10 doesn't last and they send a lot of traffic your way then you might want to pull out your wallet for that search engine, to encourage them to keep up the referrals. 

There is a two fold advantage to this - Besides the traffic you get from that engine, it is ALSO one more link that you have out there for Google to see. The more links you have, the more popular your site must be, so the higher up their scale you move. The higher up their scale you move, the more popular your site becomes, and the more popular your site becomes, the higher up the scale you go, etc... it's a vicious circle!

What I do is I have all my keywords, url, site description all ready in Clipboard Magic. (great little free program - don't know how I ever lived before I found it - you can get it here: http://www.cyber-matrix.com/clipmag.htm ) Then I sit at my computer for a hour or so and set up as many accounts as I can. 

Here is a list of some pay-per-clicks to get you started:

http://www.Ooozle.com
http://www.Anadom.net
http://www.MiteFind.com
http://www.Crosslinkz.com
http://www.Mobysurf.com
http://www.Najula.com
http://www.100Results.com
http://www.Sellingcicle.com
http://www.SSearching.com
http://www.Go40.com
http://www.Banx.com
http://www.Starts.com
http://www.HuntFast.com
http://www.Voomp.com
http://www.Zugbo.com
http://www.DirectHop.com
http://www.FastSearch.com
http://www.HeatSearch.com
http://www.Metaeureka.com
http://www.Misterppc.com
http://www.GoPile.com
http://www.Solidhits.com
http://www.Fmnl.com 

Most of these sites will stop giving accounts away once they feel they have obtained enough clients, so if you find a site in the list that is not giving away free traffic, then I would advise you to move on to the next.

You can find more pay-per-click sites by going to the search engines and doing a search. I find a lot of good ones on Ebay. They are usually brand new sites and they will auction off say a $10,000 account for a buck - I buy those a lot, but I won't bid much. (They are usually under businesses for sale, but don't go there and run up webman's little bids! :)

I think I have bought and read just about every internet marketing course in the world, there are a few I would recommend to anyone, but this one goes beyond anything I have seen:  http://www.qbug.net/goto/moneyhome   If you want lots of traffic then this site is a must read. 

I hope this helps you.