Upgrading to what stage exactly? Unless a new camera does something specific that your Sony doesn't, a new lens will do far more to expand your picture taking than a new body will, just for the sake of it. Sony lenses are very good.
If you want to go Canon, a 40D is perhaps a better bet ATM IMO. They are good value, having been superceded by the 50D, but don't forget the Nikon D90.
I'm not sure why people say Sony are restricted for lens choice. They might not have as many as Nikon/Canon, but how many do you need? Third party brands fit Sony too.