actually the Stan's Alphas are coming in around 352g for the 700c format.
There's a least one other rim besides the Aerohead that's rated @ 390g in the 650c. Mavic maybe? Not a terribly interesting rim, anyway.

The tubular 404 650c, the 330 rim, is rated at 375g.

Seemed like there was an older 650c version of the 303 wheelset, with the rim close to 325g maybe?

T