Since the release of Limera1n from Geohot to jailbreak your iphone running 4.1. Greenpois0n from the Chronic Dev team has been released. The Greenpois0n program uses the same exploit Limera1n is using. The Chronic dev team has shelved the SHAtter exploit originally planned to be released, they have saved it for future use.
The advantage of Greenpois0n is that it is available for Windows, and linux. Below are the links to the download and their website.
The Chronic dev team also announced that apple TV jailbreak is coming as well as the greenpois0n version for the Mac.
UPDATE 10-18-2010: Now Greenpois0n is available for the mac. The link is below.
Greenpois0n Website: http://www.greenpois0n.com/
Windows Download: http://cache.greenpois0n.com/dl/gp_win_rc3.zip
Mac Download: http://cache.greenpois0n.com/dl/gp_mac_rc3_2.zip
Linux Download: http://cache.greenpois0n.com/dl/gp_lin_rc3.tar.gz