I'm finally about to outlive my ATT wireless contract and am looking for the best/least expensive data plan to use with my N800. I really don't have any loyalty to any carrier, I just want my walkaround web at a decent price. thoughts?

I tried 3 carriers and here is my experience:
1. T-Mobile - cheapest if you set up your own proxy (5.99/motnth in addition to plan), but is very slow and has very bad coverage if you go outside city limits.
2. Verizon (EVDO). Unless you want to buy expensive data plan, you will use data as plan minutes. I.e. data usage on weekends would be usually free and on regular days every minute you are online counts as a voice calling minute. Coverage is good (same as AT&T in my experience) and it is pretty fast, but not as fast as AT&T 3G.
3. AT&T - very fast (DSL/cable speeds) if you live in 3G area. Decent in EDGE areas. Unlimited data will cost you $20 on top of your plan, coverage is very good.

I do not know about Sprint/Nextel - never tried those.

Sprint plans are pretty reasonable. I think $15 for power vision? Sprint seems to do less than Verizon as far as crippling DUN.

However, on the other hand, T-Mobile and ATT phones have much better battery life. (although I think CDMA is still faster -- Sprint and Verizon).

I've been very happy with Sprint and I can't believe I'm saying that about a cell company.