What is (are) your favorite firefox addon(s)?

My top 2:

1. adBlockPlus: Great for sites with a zillion ads

2. drag and dropZones: One of the best addons, its really helpfull

DownThemAll and Image Host Grabber. If you collect multimedia of any kind for the first, and like to mass-download images for the latter (though the first can do the same), these two are your best friends. DownThemAll only works with files directly linked on the page, while IHG can, for instance, go through images on deviantart where each image has its own page

Can Adblock Plus be customized? I need it for some sites i go to, but i don't want to interfere with all scripting all the time...

Fasterfox, that's it, I find they really weigh down FF

Yeah, you can whitelist sites that you don't want to block. 

On topic: 

Adblockplus: Makes this site bearable, along with a few others 
No Scripts: Keeps me safe :)
Pricechecker: Finds the lowest prices over a wide range of sites
Stylize: Keeps my firefox sexy :D
Greasemonkey: Need my scripts!

adblock and the youtube downloader

AdBlock Plus w/ Element Hiding Helper (helps a lot!)
Easy YouTube Video Downloader

That's all for now. I thought about getting noscripts, but didn't want to mess with it.

no script
download helper
status4evar
foxyproxy
fasterfox

with firefox 3 theme for FF4+