With the release of RC4 of Greenpois0n, the jailbreak tool now adds support for the iPod Touch 2G, both MC and MB models both of which are untethered jailbreaks.
pod2g tweeted earlier about his second exploit, which he calls “steaks4uce”, which exists for the iPod Touch 2G. Using this method alongside Greenpois0n, and using Comex's tether hack, greenpois0n adds the iPod Touch 2G to it's list.
Both Windows and Mac versions are available via the greenpois0n website.