firefox stuff:

errorzilla plus - it gives you more options for when a page can't be displayed.

coolpreviews - lets you preview a page before you click the link.

foxytunes - lets you control your music player from firefox

longtitles - keeps tooltips (those things you get when you hover over xkcd comics) from being cropped.

morning coffee - it'll automatically open the websites you tell it to in tabs when you open the browser

open in browser - gives you the choice of opening a document in the browser window rather than downloading it

read it later - saves pages to read later instead of bookmarking them

sxipper - pre-fills forms and logins and passwords for you

colourful tabs - makes your tabs colourful obviously



windows stuff:

windirstat - gives you a visual representation of your harddrive. I love this thing, it mkes it o much easier to see what's taking up room on my computer.

that's pretty much the only app for windows I completely swear by.