Spec me a Canon lens

[Foiled]

I'm taking the family to Disney World towards the end of June and fancy hiring a good Canon lens to capture some good pictures.

Any suggestions for which lens to get?
I don't want it too huge as I'll have to carry it round all day.
Price not a major consideration as I intend to hire it

Thanks

 

[Foiled]

It's a 400D.

Mainly family shots, and possibly try and get some Disney firework shots as well - I'll need a tripod as well for that though

Thanks for the responses