Yeah I picked one of these up last month, got one that came with 2 batteries. (Third party)
Extends battery life so I can get a full days shooting. It's made for the D40 I think, so doesn't fit the contours of the D5000 exactly, but I'm not too bothered about that.
It has a little compartment to store the lid from the original battery compartment. (If that makes sense)
Also the one I have doesn't have the little lead for using it in portrait mode. Instead you just select the wireless remote setting from the menu and it works from there.
Grip and batteries bought from Ebay for £37.95 delivered.
I'll try and find the link to them if you want.