I use the recent Ganymede release of Eclipse, specifically the distro for Java EE and web developers. I have installed a few additional plugins (e.g. Subclipse, Spring, Find
Eclipse by itself is pretty bloated, and the more plugins you add only exacerbates the situation. It's still my favorite IDE, as it certainly isn't short on functionality, but if you're looking for a lightweight IDE then I'd suggest ditching Eclipse; it's pretty normal to run up half a gig of memory if you leave it running for awhile.