If for some reason, you don't want to get the new iPhone 4S, Apple retail stores are selling the remainder of their iPhone 4 16GB and 32GB models while supplies last. The clearance prices for the units are $149 and $199, with the usual 2 year contract. Apple will offer a $99 iPhone 4 model going forward, but that model only has 8GB of storage.
The prices are $50 and $100 cheaper than their 16GB and 32GB iPhone 4S counterparts, though you are losing a fair number of features (faster processor, Siri voice assistant, better camera).
Article Link: Apple Clearing Out the iPhone 4 for $149 (16GB) and $199 (32GB)