I'm using RockPlayer Lite version 1.6.3
I'm almost positive I've viewed avi files on my gtablet.. however, as I convert some full movies, I've done so to mp4
I remember reading somewhere that some people had issues with RockPlayer when file size got too large.
Current: RAZR MAXX, Nexus 7, Droid Bionic - Stock, Nabi 2
Older: Charge-Tweaked v2.0, OG Droid-Pete's Bugless Beast 0.6.2.1, g-Tablet-VEGAn-Tab GingerEdition STABLE RC1