f0recast is a new tool, currently under development, from iH8sn0w that will help you figure out if you can apply a tethered or untethered jailbreak to your iDevices. All you will have to do is connect your iPhone or iTouch to your computer and load the application.
According to iH8sn0w, the tool is in its final development stages, and it should be released in the next couple of days. Once released, the tool will probably be pulled down, and get a couple more updates in the first day or two.
This tool is extremely useful, especially for new jailbreakers, but incomplete. Once you establish the nature of the jailbreak you can apply, it would be nice if the tool would tell you which tools you can use and also give you a link to download those tools.