I use this one. There's also a 60 lb version available if you don't usually ship heavy packages.
Also, when you're entering shipping weight on eBay, always round up at least a few ounces. (For <1 lb, each ounce costs a bit more, over that it's done by pounds. So 2 lb 3 oz costs the same as 2 lb 10 oz.)
I have this one that works great and only costs $26. Also comes in black for $24