Multisite - admins can't see Plugins menu, help!

When my users login to their wp-admin for their sites on my multisite network, they don't get any Plugins menu in their admin area. The option just isn't there over in the left-hand menu. I've checked my users and they are all set up as Admininstrators. I have no idea what's happened... any ideas how to fix this? I had played around with Admin Menu Editor plugins a while back, but they are all deactivated now. Any help apprecaited.