Consumer Reports gave their Best Buy's awards to these grills:
Medium size:
Vermont Castings VM400XBP ($400, Home Depot) - this model does not have a side burner
Char Broil Advantage Series 463453305 ($200, Lowes)
BBQ Grillware: GSF-2616 ($200, Lowes)
Large:
Great Outdoors Pinnacle TG-560 ($500, Lowes)
Char broil Commercial Series 463251705 ($500, Lowes) - This one is rated excellent in every catagory, is all or mostly stainless, has premium grates, and lifetime warrantied burners
The Weber grills they reviewed were 6th (in the Medium catagory, for the Genesis Silver B) and 5th (in the Large catagory for the Summit Gold, which is $1350)
If your budget is $500 and you need the cooking space of the $500 weber from Lowes, go with that one. Otherwise, there's a model right below that in size for $400 - the only discernable differences besides the size I could see was that the side burner on the $500 one had a brass cap on it and the larger grill had one more main burner. The $400 model was the one I bought for my parents, it's more than large enough for them.
According to CR, many stainless grills use a lower grade of stainless steel (all the ones they gave CR Best Buy Awards to had this lower grade). They're slightly more likely to corrode according to the tests that CR did (when compared to the higher grade of stainless steel), so buy a grill cover too (the one I picked up was $13). If you want to tell if the stainless steel is 300-series, bring a magnet. 300-series isn't magnetic, where 400-series is.
Those prices are for propane grills, natural gas (at Lowes at least) was $50 more.
(edited for more info on stainless-steel quality)