iPod Touch 3G – iPod3,1_4.1_8B117_Restore.ipsw
iPhone 3G – iPhone1,2_4.1_8B117_Restore.ipsw
iPhone 3GS – iPhone2,1_4.1_8B117_Restore.ipsw
iPhone 4 – iPhone3,1_4.1_8B117_Restore.ipsw

Remember, there isn’t a jailbreak for 4.1 yet, though the boot ROM does have a hole in it, which means it will be quite hard for Apple to close. 4.1 also updates the baseband (modem firmware), so if you rely on a carrier unlock, you’ll want to avoid 4.1. TinyUmbrella has an option to upgrade to 4.1 without upgrading the baseband, but it only works on the iPhone 4 and there is at least one report of it not always working. The safe move is to just wait on the upgrade for now.