Perhaps this already exists, but I don't think so. I would like an AddOn to extend my chat frame. AFAIK, there is a default max width it can be set to and I'd like to override that making my chat frame wider.
Would like to see the same thing for the minimum width...
Anywho, you CAN actually do a little hack to get around this... Just go into your layout-cache.txt file and manually set the width you want. It's not pretty, but it works. Just don't unlock and try and manually change the size in the game, else it'll reset back to the old limits.
Maybe I'll poke around and see if I can come up with something simple, but the blizzard chat frames scare me and I'm kinda afraid to mess with them too much.
There's an AddOn called Chat Frame Extender at http://ui.worldofwar.net/ui.php?id=1506 which I belive does what you want and then some. I'll leave it to someone else to judge whether or not it should be ace'd :)