Actually I don't really see much sense in converting videos. Nowadays you can use a cheap network media player like WD TV Live that allows to play videos from a USB Flash drive, portable hard drive, from your network,...

You may need to remux FLV files into MP4 or MKV files for using on such a player, but this can be done losslessly, fast and for free:
FLV to MP4: Remuxing FLV files with freeware FLV Extract and mp4box / yamb