Making sigs for gaming clans was how i became interested in graphic design. It's good for learning photoshop but thats about it. The size and usually the request are all the same. You'll get bored quickly. Move on to bigger pieces. Try wallpapers or posters for your room. For 13 your doing great, your about the same age i was when i started doing sigs. Get some good books on design and you'll open up a whole load of inspiration for yourself.
Good work though. You've taken me back to delta force 3 days.