I am right there with you needing new baking sheets. While I haven't bought new ones yet, I was looking at the Fresh Chalk baking Guide: freshchalk.com/d/home-bakin.... She recommends the Chicago Metallic Bakeware ones. They seem pretty standard! I think thats what I will try.
Yes, I really like Chicago Metallic: they're sturdy, long-lasting, and readily available. If price is an issue, you can get less expensive half-sheet pans at Costco Restaurant Supply in Lynnwood but I'm not sure of the brand.