File Management

Tineye
Reverse image search tool. Great for finding the original source of a graphic.
http://www.tineye.com
GitHub
Source code sharing website.
https://github.com/
ZamZar
Convert any file type.
http://www.zamzar.com/
Printer Friendly
Make any webpage printer friendly
http://www.printfriendly.com/

Fonts

Font Squirrel
Free font library
http://www.fontsquirrel.com/
Da Font
Free font library (slightly less reliable)
http://www.dafont.com/
Lost type
Stylised fonts
http://losttype.com/
What the Font
Backwards font lookup
http://www.myfonts.com/WhatTheFont/
Google Webfonts
Google webfonts
http://www.google.com/webfonts
Web Design Ledger
Some funky free fonts
http://webdesignledger.com/freebies/
The League of Moveable Type
A guide for interesting modern typeface
http://www.theleagueofmoveabletype.com/

Graphics: Design

Muro
Create attractive graphics and designs
http://muro.deviantart.com/
Pixlr
Create attractive graphics and designs
http://pixlr.com/
SumoPaint
Online software like photoshop.
http://www.sumopaint.com/app/
960.gs
Grid system for designing websites 
http://960.gs/
Subtle Patterns
Patterns and designs for backgrounds
http://subtlepatterns.com/
Squid Fingers Patterns
More patterns and designs for backgrounds
http://www.squidfingers.com/patterns/
Din Pattern
Even more patterns and designs for backgrounds
http://www.dinpattern.com/
Go Media
Vectors, mockups and templates (and tutorials)
http://arsenal.gomedia.us/

Graphics: Schemes

Colour Calculator
Check Hex/RGB colours for web-publishing
http://drpeterjones.com/colorcalc/
Colr
Colour scheme and website colour extracting site
http://www.colr.org/
Kuler
Adobe Photoshop's colour scheme service
http://kuler.adobe.com/
ColorLovers
Colour pallets and design suggestions
http://www.colourlovers.com/

System Tools

What is my IP?
Google does this too now, but I like the little guys.
http://www.whatismyip.com/
Down for Everyone?
Check if a website is down for everyone, or if it is just you that is having trouble.
http://downforeveryoneorjustme.com/

Usernames

BugMeNot
Usernames/passwords for sites requiring registration
http://www.bugmenot.com
Temporary E-mail
Temporary e-mail for when you want to sign up for something and not get spammed.
http://www.mailinator.com/

Utilities

Acronym Finder
Acronym finding tool.
http://www.acronymfinder.com/
XE
Currency exchange checking service
http://www.xe.com/
Time and Date
Meeting time planner
http://www.timeanddate.com/