Things to do in Sydney? Please help!

Hey guys/girls, A couple of friends and myself are heading over to Sydney over the month of January and we are wondering what some of the must see/do things are! We have money (but we would prefer not to be dropping mass loads of it on every little thing) but we were curious as to what any of you would recommend. We're thinking of doing the bridge climb and taking surf lessons but every website recommends really touristy attractions and although that isn't bad we would like a mix! So if you could, please help!