Compression socks are the only thing I know. Moving around doesn't seem to help; my legs swell just as much when I'm walking around a lot.

I use 15-20 mmHg compression socks that go all the way up over my calves.

Edit: You'll also see them called "support socks". Mine are Therafirm Core-Spun socks, and I bought them from footsmart.com for about $22 / pair.