Also, I stopped using Quicksilver because - is mucho used in Eclipse, and with Tiger spotlight is very nearly there anyways

Witch looks interesting. In terms of windows and tabbing, I have gotten used to Command-Tab to switch between applications and Command-Back quote (Tildy) to switch between windows within an application. However, for a new Mac user, I can see how Witch would be a big help.

I also use Aurora as my alarm clock when I am on the road.

One more app that has become essential for traveling is Noise a pink noise generator that helps block out strange hotel sounds at night. (of course, Noise and Aurora don’t really play well together ;-))

A pretty good list, I will need to try out iStumbler and I Squint.

One thing that I quite like is Witch: http://www.manytricks.com/witch/
It gives you more of a windows style of alt tabbing, which I perfer, as I may have several textmate instances open that I need to switch between.

I also like using Aurora for a alarm clock:
http://metaquark.de/aurora/ It’s free and has a very nice simple interface.

The one app that may not be as necessary in leopard, that was needed in tiger is QuickSilver. Apple made great improvements to spotlight with leopard, so much so that I haven’t personally had a reason to install quicksilver as of yet. However that is my personal experience (YMMV).

The only other thing that I would mention, that may be too ruby centric is autotest. Autotest + Growl is one of the best tools I have come across for doing TDD.