I just put in some Sony XS-V1642A's. They fit great too if you just make sure the wires are at the bottom. The mids are much cleaner, and I'm hearing things in the highs that I couldn't make out at all before. But sadly, the bass is not noticably better. Fortunately I got them very cheap.
The Sony covers don't really cover the hole, but that's OK by me--I wanted to use the stock speaker grills anyway to keep the stealth look.
I also put in a Sony CDXGT210 deck. It's not high-end equipment, but the controls are easy to use while driving, it looks clean, and it has both an MP3/WMA CD player and a 3.5mm line-in jack for an MP3 player. It fits nicely in the dash, and the green-lit buttons match the green dash lights. Too bad the bright blue screen isn't yellow, but it's fine.