packages broken on us.archive.ubunutu.com for main?

[James Carroll]

I'm getting the following on a few packages today:

W: Failed to fetch
http://us.archive.ubuntu.com/ubuntu/pool/main/libp/libpng3/libpng12-dev_1.2.8rel-1_i386.deb
  MD5Sum mismatch

png, jpeg, and nvida's glx packages...

I've waited an hour and re-tried, so I don't think it's a matter of
being half way through an update on the server...

Is there an alternate server I should point my sources to?

right now I'm us.archive.ubuntu.org (or something like that.)

-Jim