I'd say look at AWeber as well. Their "hover-over" forms technically aren't pop-ups and will get through most pop-up blockers.

And--for what it's worth--with AWeber forms you can designate how long the form waits before it pops up or drops down onto your site. I've experimented a bit and found if I delay the form for about 15 seconds, it gives the visitor just a bit of time to see your headline and main pitch.

Some people see a pop-up that blocks the main part of the page and click to leave before they get a good idea of what you are offering. You can experiment a bit, but the delay time will make a difference in the number of quick click outs you get. Good luck!