I use Eclipse for other purposes than Java development (Python, TeXlipse), and I found that the slimmest download that works for me is the "Platform Runtime Binary", sitting at mere 50 MB. Your plugin will pull anything else that it needs for installation, so quite a few plugins will probably need to be installed anyway. This guarantees, though, that no superfluous plugins will find their way into your system.
Hunt it down from the list here, for the currently latest version:
Since you didn't specify platform, I can't give you a more direct link. You will need to hunt it down from the rather long-ish list.
It's a bit tricky to find this page from the start page. You need to go to Projects->Eclipse Platform->[Pick release/build]->[Find needed package]->[Pick OS/Platform]
There might be an easier way to do it, though.