I use the plastic wallet things, and I find them really easy to re-sort every so often (quite often!). I have been through various forms of categorising but have now decided that alphabetic is going to be easiest (except for the ones I want seperate for a specific reason, eg not yet learnt, or lyrics with no tune/chords or songs with spinning/weaving connections). I don't put them in a folder, I just tie up the plastics by threading wool through the punchholes.Then I put them all into an a4 sized shoulder bag. Eventually I will cross-index them by various categories (maybe). Works so far anyway.

Kris