I know there have been numerous threads about speaker upgrades, etc., and I've learned quite a bit in reading through them.
I thought I'd give back a bit by adding a couple of pics of a recent tweeter upgrade I did. The stock speakers were replaced with 2 sets of JL audio C5-650's along with a head unit transplant, but I was never quite happy with the sound of the silk dome tweeters that were part of the C5 package.
In looking for alternatives on eBay, I came across these, again by JL audio:
I was surprised by how much better they sounded than the silk dome tweeters: they have a much more crisp, clear sound, but not at all harsh.
Both sets of tweeters fit neatly into the stock location, although I did need to use the carcass of the stock tweeters to mount the C5 tweeters. All in all, well worth the $129.00.