Ange what is deadline? I remember several friends having to get lump sum of money in fairly early on. Friend's DS raised money for trip to Africa (Uganda I think) by selling quiz sheets, cleaning cars, dog walking etc etc. I could email you a quiz sheet if you want. (people like to buy these to do over Christmas and New Year I did one at DS2's school last year and went down v well)
Another friend organised a quiz night, and wrote to local shops for prizes. Was big well known charity and because of that she got some good prizes.
Bake cakes to sell to neighbours (get them interested by delivering freee samples with accompanying price list).
Think importaant thing is to spread the word. Many peolpe are imrpessed by someone running a marathon, and want to sponsor you. When I did it in 2007 I was even sponsored in 2007 by someone I had never met - a friend of my mums. DH was sponsored £1 a mile by my colleague and her partner, and at that stage he had not met either of them.
Because so many poeple sponsored me I thought it was very important to keep a note of everyone and let them know how I got on.