It's not just Earthworm Jim 3D on Xbox Live Arcade today, it turns out - NeoGeo Battle Coliseum is also available.
Battle Coliseum is a tag-team beat-'em-up originally released for the European PS2 in 2006. The Xbox Live Arcade version costs 800 Microsoft Points (Ł6.80 / €9.60).
It brings together a range of characters from SNK franchises to smack each other about - so if you're a fan of King of Fighters, Art of Fighting, Samurai Shodown, Fatal Fury or even stuff like World Heroes and Metal Slug you'll probably recognise someone.
If you're interested you can grab it off the web-based Xbox Live Marketplace, and of course there's a trial version.