Superkaramba needs some work IMO, but if you are using KDE, i recommend it, otherwise gkrellm is the best of the best, all IMO of course, it is pretty much personal preference but Superkaramba has a tendency of occupying more resources (and has had a few loop errors and memory leaks, probably resolved since i tried it so pay no attention) than gkrellm if you are not using KDE (probably works the same way around with gkrellm, i haven't checked).
IOW, this post is useless spamming, gkrellm is the best.