Redsn0w, the popular iOS jailbreaking method for the iPhone has just been updated to version 0.9.9b1, available for both PCs and Macs. It brings a ton of new features and fixes, among which the most important is that you no longer have to download the entire IPSW (except if you try to jailbreak iOS 5).
The official changelog is pretty impressive and you can check it out by following the source where you’ll also find the links to download the apps. The current version of Redsn0w, according to the official description, “fetches pieces of public IPSWs from Apple (once). Non-public IPSWs must be provided manually (once). It then caches those pieces for future use.”