A varied assortment of links to sites I've found interesting, in no particular order...

Apotylon Civilization Site - for Civ'ers everywhere.

Microprose

Dragonchess rules - Andrew Jackman / Hans Bodlaender

The Creative World of Gary Gygax

Olik's AD&D Pages - vast quantities of AD&D material.

Sebastien Martin - compiler of the AD&D NetBooks.

Discover Magazine

Extrasolar Visions - Planets discovered orbiting nearby stars, with artist's impressions.

Urban Legends Archive

Computer Stupidities - Hilarious tales from the Tech Support front.

The Adrenaline Vault - huge computer games site, with many downloadable patches, map editors etc.