the new gameboy is out already, iirc, it's the Gameboy Micro, or something like that. Other than being smaller than the original, I don't know what else it brings to the table.
If you want a better GB, get the Dual Screen. Although there aren't many games designed for the system yet, it's an improvement over every other GB in that it's backlit. The screen is a *hair* bigger than the older models, but games that aren't specifically desinged for the DS will appear in a sort of letterbox format. The DS has already been discounted down to $129.00 from the launch price of $149. You can *only* play Advance and later games on it, iirc...so your real old GB shit won't work.
I had one...boxed it up and sold it right after I got my PSP. Not a bad little sytem, but the first time you see the PSP, it pales by comparison.
Still, I'll probably get another one down the road...the backlighting is nice, even better than the old one with the Afterburner kits, imho.