You should get some good lens first! Trust me, you will be force to upgrade your body later. Same to me, I bought a 24-70mm f/2.8 L on my 450d, after using it for a while, the 450d doesn't coop with the 24-70mm very good, it is very front heavy since the lens is way heavier than the body. The lack of iso performance on the 450d is another reason for me to upgrade the body as well. I am using the 60d now, the mid range Dslr is way more solid on hand, better control dials, faster AF and image quality is just amazing.
If you like shooting people, should consider picking up a sigma 30mm f/1.4. On a crop camera, this is a great lens, you don't have to walk very far away to capture a little bit more things, unlike the 50mm f/1.8.
If you want a everyday all purpose walk around lens, hands down 24-70mm f/2.8 L.