As converters go, Convertzilla is small both in download size, screen space and memory usage. It supports a huge list of video and audio files including FLV, MKV, MPG, AVI, MOV, WMV, 3GP, MP3, AAC, FLAC, WAV, and much more.
You can use select to find the file you want to convert, or drag and drop any file into the application. Then you just choose the format to convert to and optionally decide if you want to modify the quality as well as size for video files. Click on convert, and you're done. It doesn't get much easier than that.
Presets are available for Android, iOS, Windows Phone, iPod, Blackberry, Sony PSP and PS3, Microsoft XBOX 360, Zune, Chrome, and more.