Help! Need Ideas 11yr Old`s Party 25 Kids Invited!

Help! My daughter and I are trying to come up with a great party idea for her 11th b-day!! Its her last yr in elementary school with all her friends so she wants it to be really special and decided to invite the whole class!! We are doing it in the backyard but that is about all we have decided so far!! Please if you have any ideas at all that would be wonderful!! Either post them here or email me direct at kjb2003@msn.com Thanks in advance!!