From my experience, you will always find bands that want a good looking film of them performing, especially if you can get it looking as good as possible for use on their My Space page. The problem that I have run into on a number of occasions is the venues. A lot of the big venues in London don't like people filming gigs unless they are going to be making a little something extra out of it.

Places like the Jazz Cafe and the Astoria will happily pluck a figure out of thin air and it's usually pretty high! Make sure that if the band has agreed to you filming them and you've drawn up the contract, that it clearly states who is going to cover any fees asked for by the venue. I've turned up at a few gigs only to be turned away by the management...

Another good thing to try is to be exceptionally nice to the staff at the venue - this can sometimes gain you access to "off-limits" parts of the venue such as balcony area's if you're lucky...

Sound wise, always see if the band can get a copy of the sound from the desk - most sound engineers will be able to make a copy of the gig in some way, even if it's a tape that you end up having to do a bit of cleaning on. It will help when you have to cut out drunk fans shouting at the camera after a few beers

Good luck with the business and feel free to PM me if I can be of any help...