In an recent update at www.tf2.com Valve announced that they are taking submissions for user created weapon and hat models. If your submission gets accepted you get to use your item right away and others have the chance to find it randomly in game.
If you’re not a 3D whiz, and you find that good ol’ 2D graphics are more your thing, then you can also create your own avatars to go on the official TF2 Steam Group, available for download by all.
Valve give guidelines on creating the content for the game and an easy to use submission form. Click the picture above and all will be explained.
You can find out how to make hats for tf2 on the steam forums.
Hi, I'm Dash. I've been with total oblivion for about 5 years. I'm proud to be part of a gaming community like this and I'm still amazed when our European members fly over for the usual summer LAN. If you're in Europe and you're a fun gamer with a mature attitude then we want to know you. :) 
Just as an FYI, a bunch of player-made hats, weapons etc were released into the game a while back. Let us know if you have been lucky enough to unlock any.