Summer Player used to be VPlayer Advanced until it was yanked as it was too confusing with a different VPlayer (previously reviewed).
Summer Player is a VERY good video player as it can browse for video and other media files, scan your SD card for media and present a list, or just receive "intents" from other apps for playback. It plays FLV files very well, even files that other player apps have problems with. It also plays back a TON of other media formats, including the relatively obscure RMVB.
If you insist on only using free apps, Summer Player is the BEST AVI and video player available.
Rating: Get it!
http://www.appbrain.com/app/summer-player/summer.video.movie.music.player