Even after 5 years I still put this on all my 4 rigs and every Windows installation:http://www.desktopsidebar.com/
Their lead developer was hired away by MS to develop the Vista sidebar and they've shut down their forums *sniff* but it's still far superior to anything else out there. I am using it on XP, XP 64, and Vista 64. There are just a few compatibility issues on Vista with some of the third party plug-ins.
Especially with the newer widescreen laptops you hardly notice it, and you can hide it anyway so it slides away if you want. I keep mine at less than 1" wide. It used to be a bit of a resource hog but, again, with the newer systems and their higher speeds and memory it really doesn't matter.
I haven't tried it on W7 yet, which I just installed last nite.