There are quite a few options out there for rocker covers for the LS1 now. Cast alloy, Billet aluminim, fabricated sheet aluminum and even carbon fiber are now readily available.
With the strength of the $$ at the moment now is the time to buy.
I've got the GM Performance Parts valve covers. I got them through Speed Inc:
GMPP Valve covers
Here's a finned style:
PML Valve covers
These guys have a variety of billet and fabricated rocker covers:
Nasty Performance
These guys are doing carbon fiber:
Scooters Performance
There's others out there. These are just a few.
Cheers