Ok, here we go. This, I'm pretty sure, isn't all of them; back in my really early days (late 2001, early 2002), I never really hosted my own images and relied on the kindness of the people who made the sigs for me. However, these are the ones that I found sitting around in my folder (these are in no particular order).
(Made by Glenn)
(Made by Magus, I think)
(Made, clearly, by Chimpbot)
(Made by Android 16/Sonic/Lee, not the same Lee that we know as Mad Axman)
(Made by MinesSkylineR34)
(Made by Owa)
(Made by Chimpbot, as well)
(Made by The Professional)
Plus, of course, the one currently in my sig (essentially the same as the one above, just without the shiny effect on the text). I also recall having another Mega Man one, as well as my first one, which was some random Vegeta images plus the phrase "The Majin is Coming", which the artist chose to include. I also had a sig I made for myself and, thankfully, have lost =P