I second Ruby, Rails and JQuery, it's like the holy trinity.
Aptana Rad Rails is very good, love the syntax checking.
jQuery UI - I love it, theme able Rails Apps! But honestly, I've never re-themed any of my apps, one day maybe! Also, a canned UI may just not be your style, or remember Motif vs. OpenLook?
pdftk is OK, kind of old, doesn't do some stuff it should, (i.e. can't combine two pdf's with same form field name, then later fill the combined forms and get both fields filled. If you combine pdf's manually or some other way, pdftk will fill them correctly, but not if pdftk combines them!)
freetds - MS SQLServer access, works great so far!
libxml-ruby - ??? works, but searching a parsed XML Document had issues? I don't use XML searches
passenger - Rails deployment straight from Apache, sans mongrel, supposedly running passenger and Ruby Enterprise Edition from Phusion reduces memory footprint 1/3rd??? I don't know, but it worked and is convenient.
DeltaCopy - cute little Windows RSYNC tool, for pushing development site to Unix production box.
cwRsyncServer - RSYNC server for windows, for syncing up Windows dev to Windows production (yes, I have stuff deployed on Windows!) Works fine, easy setup.
Joe got a job, on the day shift, at the Utility Muffin Research Kitchen, arrogantly twisting the sterile canvas snout of a fully charged icing anointment utensil.