Ch8 Has a forum post The Best/Most Useful Vista sidebar gadget ever! , so I thought I'd share my picks with everyone else here as well.
Here are my picks for top gadgets for Vista Sidebar:
CPU Multi-Meter shows individual cores and memory, because you have to know what's up. [there is also a quad version]
http://gallery.live.com/liveItemDetail.aspx?li=f5b13626-b266-4334-b2e5-157bd66ca5af
Volume Gadget, because clicking on Volume icon and adjusting at high resolutions is too much work.
http://gallery.live.com/liveItemDetail.aspx?li=90ab2b0d-633e-4f28-8177-6d77f23852bf&bt=1&pl=1
Live Search Maps' Traffic Gadget. Do I even need to say why? [hope u live in top 50 US cities though]
http://gallery.live.com/liveItemDetail.aspx?li=d5ad423c-05bd-4de4-8803-b05ecc339397&l=1
Built-in Weather Gadget. I have 3 of them tracking city where I live, work, go to school. [long story] helps to know where it's raining.