I wrote earlier about a bad, bad experience with a Nuon brand laptop battery. I replaced that battery with a Rayovac Maximum high capacity because that other battery pretty much crapped out.
So far I've been happy with my experience with the Rayovac Maximum battery. It is kind of slow to charge, but once charged it works really well. How much charge a battery holds is the more important thing when it comes to needing to use your laptop without being connected to AC. I am getting more than an hour and a half of use from this battery.
I mentioned charge time earlier -- basically the battery takes a while to charge, but that is okay and its not painfully slow. Think in terms of charging it while you're off at a college class or charging for a couple hours to reach fully charged capacity.
It's a relatively new purchase, but so far I have been very satisfied with it. I am hoping it doesn't fail like that Nuon battery.