GBA SP All-in-One
I recently posted about a beautiful aluminum shell for the Game Boy Advance SP, though it is rather expensive. Another option should be going on sale soon, from Retro-CNC (by the way, they also sell some very nice aluminum buttons for Game Boy systems) and Makho, who's always coming up with something new. Incidentally, the battery contact plates from the battery mod article are his design.
The device looks very interesting:
The shell is not yet available to buy or preorder, but I'll keep you posted.
Update. It's now available on AliExpress.
Update: this AliExpress listing is no longer available.