We've built an Imgur album for the new Twitch banners, which must be exactly 320px wide. Feel free to use any images you find. Here is the template image (simply drop your art on a layer below):
Save the result as a flat JPG. Make sure the image links back to http://www.speedrunslive.com/
If you want to use a different color then change twitch_red.jpg to one of the following: