not sure if you are male or female etc so a few suggestions 4 u
Girly night: a sex and the city night - have the girls round and get tarted up watch sex and the city (rent the dvds if u dont have em) make and drink cocktails and then head into town
Boys night: dress as your fave super hero or make them up inc super powers then go into town - whoever has the best super powers is deemed on howmany drinks you can get bought for you or how many ppl you can snog by the end of the night!
Also works as a James bond theme night
Have a spring barbeque turn qup the cewntrasl heating and everyone think hawaiin
look for local club nights - also contact local clubs and say there are x amount of people coming out for my birthday can you do me a deal (you will often get free or reduced entry)
Go zorbing
wine and cheese party
comedy clubs (often do a deal for food and a show)
Surfing lessons
pamper session
also check out last minute.com for ideas!
Paint balling
iceskating
5 aside football - losers have to do whatever the winners want for the rest oif the day - or buy your drinks all night!
not sure if these help but havinhg done most of them they are good fun!
have a good birthday