What are some helpful tips and online resources for getting a new smartphone?

I need a smart phone, preferrably an iPhone. I don’t care if it’s just an “old” 3GS. I would settle for an HTC if its a good deal.

But I know in this market there’s ways to get a good deal and there’s plenty more ways to get screwed.

I would prefer an “everything unlimited” type of plan, definitely don’t want a data cap.

What’s the best and cheapest way to do this, even if I have to sign a contract?