Sonic Battle

GameFAQs
Includes information, FAQs, guides, cheats, reviews, downloads, and a message board.
http://www.gamefaqs.com/portable/gbadvance/data/914720.html

GameSpot
Includes information, news, screenshots, links, previews, and a review.
http://www.gamespot.com/gba/action/sonicbattle/

nGaming
Includes a collection of cheats.
http://www.ngaming.co.uk/cheats/1680.php

Open Site
Contains information and review overviews.
http://open-site.org/Games/Video_Games/Platform/Sonic_the_Hedgehog_Series/Sonic_Battle/

Sonic Battle X
Provides information, forums, guides, downloads, and links.
http://www.planetnintendo.com/sonicbattle/