Some people say they make good money with adbrite or bidvertiser. I never did but i think it depends on site.
I don't like bidvertiser, however AdBrite is really really good. You can approve all ads and choose for example only CPC>$0.70 (depends on niche).
You can try looking through my review of ad networks, just the bigger ones there atm. http://www.xenyo.com/blog/guide-to-ad-networks-for-publishers/cpc-ad-networks/
I recently began using Adbrite and Bidvitiser yesterday, so far I like Bidvertiser better - It's paying decent CPC however I have only had a few clicks so far. Adbrite isn't even displaying ads right now, while bidvitiser is. How long does it usually take to get some ads running with Adbrite??
Yahoo and MSN AdCenter are close to the results of AdWords. It all depends on what your marketing and your target. Bidvertiser didn't work for my market to well but it might for yours. I have a list of ppc sites in my sig too. Best of luck.
The hype these days is all about WidgetBucks, You can join and wait till December for payments. I guess you can earn around $4 CPM
Currently BidVertiser is the best alternative. I've tried many networks only to find this one paying the highest.
nitmech- They pass down earnings from companies and advertisers that pay them. The companies do their own audits first!! After those companies do their audits, WidgetBucks does their own audits because they have to. So, WidgetBucks is paying out a good percentage of what these other companies and individual advertisers are paying to them. Other good ppc programs are: Ads-Click.com (choose your own rpc) Chitika Adbrite