Just for the hell of it, I'd recommend a E4xxx or E5xxx series, just to get the dual core and additional cache. If your needs for that box increase, or you want to start running some server-side apps/etc, you'll have a little more power to play with. The new Celerons aren't too bad either, but is there really much of a price difference? Probably pick up something decent for dirt cheap here in the forums actually.
edit, whoops, forgot the new cellys are dual core 🙂
what the hell, the Celeron E3200 and above seem pretty decent, scratch what I said. 🙂