You won't see a ton of improvement on a stock engine with a cam swap, but that's not to say none will be had. If you're talking about doing some port work to the heads, you should look into either porting your current intake, or replacing it with a higher flowing piece (recommended). There's a guy who posts up on the 5.0 Tech side of this site named Thumper460 who sells ported E7 heads, and I know there's several members running them who are satisfied with the performance gains they saw. Do some searching around and maybe take a look at their combinations for some ideas on where to get started. I really can't recommend a cam because of not knowing what type of performance you're looking for, but keep in mind that the factory heads are known to suffer on the exhaust side, so a split pattern cam that favors the exhaust will probably net you better performance than say a B303 or E303 cam (or the like) will.