Well that is a tricky question as it depends on what style of cover you want (trifold, rollup, hardshell) LOL.
For Roll-ups, the TruXedo TruXport and Lo Pro do really well. Here is the link to all of them.
The BAKflip G2 and Extang trifecta are also popular.
Once you narrow it down, shoot me a PM and I will see what I can do for you!