Other world computing has some good ones.
http://eshop.macsales.com/shop/powerbook/b...7inch-aluminum/I have heard good things about their higher capacity batteries. You do have to pay a premium for them however.
I walked into an Apple store about a month ago and they were having one of their table sales. There was a powerbook battery on the table for $49.99. I asked if there was anything wrong with it, they said no, it was just returned, and if there was anything wrong with it I could exchange it for a brand new one. I picked it up and it lasts longer than the battery that came with my powerbook and it was still wrapped inside the box. If you have an Apple store nearby, I'd really recommend watching out for the sale, 50 dollars for a battery was an awesome deal. I stop by there every time I am in the mall now just to check if they will do it again.
Also, you can have your order shipped 2nd day air for around $5.