I use
Feedreader, but I'm considering changing. Its got a few annoying bugs, but despite that its the only one I've found that has the following attributes:
* Pop up box with headlines
and
* Doesn't need something like .net to be installed.
All the other ones I've seen have been either flat pages which need to be checked, scrolling marquee type things, Firefox live bookmarks or need .net. The good thing about having the new items appearing as a pop-up box in the corner of the screen for a few seconds is that its fairly unobtrusive (unlike a scrolling thing), but doesn't need me to go and check it (like live bookmarks).