I know some of you may consider this to sacrilegious, but a lot of programmers are subjected to using Eclipse from time to time for various reasons. For those of you that need Eclipse for a given plugin, debugging session, or what have you, the Eclim project provides a flexible solution for integrating Vim with Eclipse.
Using Eclim gives you three options for how you'd like to integrate Vim and Eclipse. The least intrusive allows you to run a headless Eclipse and control it via Vim. This makes Eclipse act as sort of an app server, which Vim can pipe to and from.
The second option allows you to run both programs side by side. This way, Vim is still running standalone, but you can control Eclipse directly should you need to.
The final option allows you to embed Vim directly into Eclipse. You'll lose some screen real estate when using this option, but it may suit certain people's needs.
I'm not really a fan of Eclipse by any stretch of the imagination, but for things like Java debugging, it does offer some utility, so if you're in the same boat, you should give Eclim a try.