There awesome!
It good that you can do a lot of different styles.
Im not a sig maker so i cant really give you any constructive criticism, but you've done a good job IMO
Thats impressive. For a while i thought about getting into sig making, but I doubt i could find the time. I may take it up at the end of the year on 8 week holiday though.
I think you need to set a better balance between your central image, because sometimes I can't tell what is the focal point. If you're going to work from the far left or the far right, I suggest adding some effects behind the person/whatever. But I'm not into graphics, just saying from what I can see visually.
I'm too lazy to give you the extensive feedback that I usually do, but long story short: you have some good stuff.
As some advice, though, you will get much better feedback at the "Official Graphics Comments & Criticism" Thread, as more people check that thread and more often.