Tracking user logins

What would be the best plugin for tracking user logins in a WP3.0 network (note: for a variety of reasons I can't track by IP, I actually need to track their user login)? I see some that track user activity such as comments or posts, but I actually need to track whether or not they logged in, not whether they add content. I've tried the "Login Logs" plugin, but it doesn't work in WP3.0.

Thanks,
Jana