Most stable so far:

Donkeymails Low $1 Payout
http://www.donkeymails.com/pages/index.php?refid=msanichar


Aqua-Mails - $3

http://www.aquamails.com/pages/index.php?refid=msanichar

GombolPTR - Low $1 payout
http://gombolptr.biz/pages/index.php?refid=msanichar

CashDelight been around MANY years and still paying!
http://www.cashdelight.com/pages/index.php?refid=msanichar

AdPaid - I have been a member since 2004 and they always pay within 24hrs
http://adpaid.com/pages/index.php?refid=msanichar