Simplehelp has a handy article - 20 Free RSS Readers Reviewed ("rss reader" = "aggregator"):
Now that almost everyone knows what RSS is, I figured I’d review a few of the ways you can read RSS feeds. With a heavy emphasis on cross-platform and/or open source, here are 20 (albeit somewhat brief) reviews of the free RSS readers available. Links to download, screenshots and system requirements are included with every review.
[via Janet Johnson]
If you are getting tired of the aggregator you are using, this could be a useful starting point. Be aware that the reviews are a few sentences with several screenshots of the aggregator in action.
Of the applications reviewed, 3/4 are client apps (install-on your machine) and the other 1/4 are web-based apps. Of the client applications, nearly half operate on several platforms. Of the rest four are Windows-only; two Macintosh-only; and two Linux-only.
Sadly, the platforms reviewed don't include some of my favorites: GreatNews (my current aggregator) and SharpReader (for threaded views - though RSS Bandit is reviewed, which also does threading). In looking at my FeedBurner stats, the review certainly covers the big readers. Interestingly, My Yahoo shows up as about 2% of applications used to read my feed.