Wizards of the Coast. All the stuff to play D&D, product information, the original character sheetsfor download. Check out the D20 System Reference Documents or the Previous Edition Downloads. The AD&D version of the Forgotten Realms books are much more detailed then the current edition.
Download the 3.5 SRD as offline-searchable HTML-documents or Windows-Helpfile or as a database. Useful!
The unofficially revived Planescape Campaign Setting for 3rd Edition rules.
The most comprehensive compilation of the Forgotten Realms-timeline I know, as a printer-friendly PDF.
Yet Another Forgotten Realms Web Page - A lot of information about the Realms and especially Waterdeep.
An nice collection of useful SRD-tools with generators for names, encounters, items and so on. Even complete dungeons...
Other Character Sheets
A vast number of sheets for different systems. The D&D sheet was an inspiration for my own.
A neat sheet with a great and complete and dynamic spell list attached. Nice work...
Giant in the Playground's "Order of the Stick" webcomic. Great.
The Ministry of Abnormality proudly presents "Commissioned". Also great. 7 days a week.
Tony Moseley's Zogonia comic strips, as seen in Dungeon Magazine and Dragon Magazine. Absolutely hilarious.
Dire Destiny Fantasy Webcomic.
RPG-Related Stuff and Honorable Mentions
Everchanging Book of Names - A cool name generator, with has sets including Forgotten Realms races. (Shareware/W32)
The offical soundtrack of the MMORPG Lineage II for free download. Really great ambient, orchestral music. (There seems to be no downloading possible, but still streaming. Damn.)
A nice tool to trigger samples and music with keystrokes, useful for GMing. Open Source for Mac OSX. (Open Source/OSX)
Tony DiTerlizzi, in my opinion, the best illustrator around. He has a fantastic imagination and has done wonderful works for the both discontinued campaign settings "Planescape" and "Changeling: The Dreaming".
Other pages I deem list-worthy are available via stumbleupon