I am chairperson of PTA (but we call ours PFA, which stands for parents and friends association as teachers do not generally get very involved at our school). Every parent at our school is automatically a member of PFA, but how involved they become is up to them. We generally find the same few parents come to every meeting and do all of the organising but lots of parents are willing to come to events or donate raffle prizes etc.
Some events we held last year or doing this year are, family disco, sunday afternoon treasure hunt in the car followed by refreshments, family bingo, quiz evening with fish and chip supper, adult summer ball/dance, halloween disco (fancy dress), duck race on local river, race night and our biggest earners are the summer and christmas fayres.
We are also about to start sending out a monthly PFA newsletter with news on how much recent events raised, what events are about to come up, what we are raising money for, when we need cakes or raffle prizes etc and we will also 'rent out' space on the newsletter to parents who would like to advertise their childs bike for sale etc.
PTA's are about raising money, but they are also about getting parents and kids to socialise especially new parents.
Also PTA needs to be a registered charity if you raise more than about £500 per year (not sure on exact amount, would have to ask our treasurer.)
Info can be found on the National Confederation of Parent Teacher Assoc. website which i think is www.ncpta.uk.org.
Good luck to everyone, i'll be watching this thread if anyone would like any more info.