Just bought this case on Ebay from the seller daydeal.
XMatrix Back Cover for HTC EVO 4G, Black/Grey - HTC EVO 4G Skin Covers
It was on $8.49 on Ebay, not $15.99 as it is listed on the link.
Here's a white one.
White XMatrix Snap-On Back Cover for HTC EVO 4G - eBay (item 400174136318 end time Nov-24-10 17:36:08 PST)
Currently using the OEM rubber case I got from Sprint. It's too rubbery for me and I have a hard time getting it out of my pocket. Hopefully this new case will fix the issue.