The best one I found is WiFiFoFum, which is a port of a PC program and it shows you almost everything you could ask for. When I was running it there was only an iPhone / iPod touch version but it ran fine on my iPad. I haven't tried a 4.2 jailbreak yet so I can't comment on app compatibility with newer firmware versions. I had a second one as well but I am drawing a blank as to what is is called.
