Mario Kart Double Dash

GameFAQs
Includes information, reviews, FAQs, guides, hints and a message board.
http://www.gamefaqs.com/console/gamecube/data/516710.html

GameWinners
Provides secrets, hints, and time trial records.
http://www.gamewinners.com/gamecube/MarioKartDoubleDash.htm

Mario Kart Double Dash
Offers cheats, guides, FAQs, news, reviews, and a message board.
http://cube.ign.com/objects/016/016574.html

Mario Kart Time Trials
Information, tips, and time trial records.
http://uk.geocities.com/josh_rocks_03/

UnderGroundOnline
Includes a selection of secrets and unlockable bonuses.
http://cheats.ugo.com/cheatdisplay.php?gameid=20156