If your previous sponsor had rules about targetting a new window then they must have been a text or blind link sponsor. If that is what you want to keep using then try this. You can link to these guys any way you want:
http://php.offshoreclicks.com/cgi-bin/ref.cgi?referral
I think every per sign up sponsor lets you target a new window.
If you want one with tons of free content here's a good one:
http://www.soulcash.com/index.htm?sc9evildick