We've seen the Palm Pre accidentally advertised for $99.99 before, but if you'd like a legitimate $99.99 deal then head over to LetsTalk. The company is offering the Palm smartphone for $99 after a combination of mail-in and instant discounts, though you'll seemingly need to order before the end of today if you want to be eligible.
The Pre in question is new (rather than refurbished) and requires a two-year agreement with Sprint, but that's no different to what the carrier themselves (or Amazon) expect of you.
No telling what deal - if any - the company will be offering once this particular rebate expires, so if you're temped by a Palm Pre then best to head over there now. The phone itself should ship on August 5th.
Palm Pre unboxing: