Sigma 24-70mm F2.8 EX DG Macro

Hi, I'm looking to put down the EF-S 18-55mm soon. The IQ, focal range, focus, and maximum aperture isn't working for me. It's not bad though, from 18mm to 55mm. It's just the aperture, most of all. I'm looking for a cheap lens upgrade (sorry no L glass like the 24-105, 24-70, 17-40. I would buy it, but I'm looking for something cheap for now!). Looking for a good walkaround lens, that gives me landscape and standard telephoto portraiture/low light photos.  I'm really looking for: 1....