I have use the Weber Exterior Cleaner on my 2013 Performer and it was OK. It cleaned the light stuff but didn't do much on the really greasy or "baked-on" build up.
A buddy of mine recommended Krud Kutter Cleaner/Degreaser. Spray it on let it sit and the build up just wipes of. It's water based, biodegradable and NSF certified for food prep areas.
Sorry for the infomercial but this stuff works great. I think Lowes has a 2 pack on sale for about $7.