The Sigma AF 70-300mm APO macro lens is okay lens. Nothing really stand out. The Canon 55-250mm EF-S IS lens maybe better (if the extra range is not that critical) But it is $280 at Adorama
For me, the 50mm f/1.8 is pretty sharp for the price. But personally, I think it is not wide enough. But I still like it a lot.
Also, Tamron AF 17-35mm f/2.8-4 Di LD seems to be pretty good for the price. Adorama sell it for $289 after rebate
But $280 + $290 is equal to $570 already. That leave you $430 for the camera.
For me personally, I will get the camera body and the Tamron AF 17-35mm f/2.8-4 Di LD $290 or Tamron SP AF 17 - 50mm f/2.8 XR DI-II LD $420 and save more for a good telephoto zoom such as the Canon 70-200mm F4 L $600 and add a 105mm Sigma prime later. But since the 50mm f1.8 is so cheap, so I need to get that as well.