I've bought a few from batteries.com -- I always get the ones made by batteries.com since they are cheaper and the same specs and have a couple years of warranty.
ebay.com is your best choice. I've purchased number of batteries for different laptops and never had a problem. Just today I got new battery for my Inspiron 700m using it now posting this. Original Dell battery paid around 40% from the original Dell price.
It is original Dell 71 Whr battery. More capacity than my original 66Whr. It is second generation of 700m 710m batteries (after recall). I paid $53+$11 shipping. For $64 can not be a better deal.
I am not affiliated with the Seller in any way, but here is the link http://stores.ebay.com/Portable-Components:)