Well... technically, you could buy a XOOM right now and not pay monthly for it. Just use it as a WiFi only. But you'd be paying an extra $200 for the cell radio.
On March 28th... a mere two weeks from today... Motorola will release the WiFi only version of the XOOM. Same great tablet sans cellular radio. It will retail for $599.
If that's more than you planned on spending, I'd probably wait rather than buty one of the non-Honeycomb tablets available now. There will me several Honeycomb tablets released in the coming months that will offer WiFi only.
Good luck with whatever you choose.