AFAIK the VX rims were the lightest, 13" cast aluminum. Almost exactly like the HX, but 1" smaller.

HX - 11.75lbs
13" steelies - 16lbs
14" steelies - 18lbs

perspective
15" SI - 16.5lbs
15" Rota Slipstream - 11.8lbs

I don't know what the VX rims weigh but I held a VX in one hand and a HX in the other (with tires) and the VX was noticably lighter.