Loyaltepays and Readerspaid (sister sites) are great - you get 1 cent per ad clicked and much more if you fill out the forms - 28 cents for filling out your email address is common. just register for a separate email account before joining:
LoyaltePays > Home

Donkeymails - huge - i just use the money for ads to the members:
DonkeyMails.com: No Minimum Payout!

Hits4Pay - get about 2 cents per email - they give you $10 free.
Hits4Pay - Earn Extra Money for free. Get paid to read emails online. Earn money from home. Make money on the internet, make money

Solo-Ads - get 5ents per email click - good toward advertising on their site - its a great way to test ads:
Ezine Advertising: Solo-Ads Ezine - Free Solo Ads

Thats it for now - but hey - you won't make millions but the free ads is worth the few seconds it takes to click the emails.