EditCSS is an *amazing* plug in for FireFox (and other Moz variants) that I just discovered. It allows you to edit your web page's CSS in the left sidebar and watch the change in realtime in the browser pane. This is as cool as it gets in web design if you ask me.
I just was playing and added a grey background with padding to my blockquotes, which I think looks pretty good. I was thinking about doing that at some point, but being able to just pull up my *live* site and edit the CSS and see the change in realtime is just unbelieveably cool. Check out the screen shot above, I just messed with a bunch of options until I had something very different from my current design.
Being able to see a cool-ass design on another site and being able to simply click control-8 and see the CSS and be able to experiment is also insanely cool. Combine this tool with some basic CSS knowledge from W3Schools.com and you're styling.
UPDATE 06/24/2005:: Hey Kos readers! I actually use the Web Developer Extension now instead. Does the same thing and more. Enjoy!