Sigma 12-24 f/4.5-5.6 EX DG ASHPHERICAL HSM

This is probably my most used lens. It is great for most landscape and architectural shots and also very useful if you want a nice quirky photograph.

Great vibrant image quality, nice colours and a very bright image. There is some vignetting wide open (as I use it on a full frame) but nothing that can't be fixed.

The biggest caveat with this lens is the bulbous front element. It is impossible to fit any filter over the lens, so great care needs to be taken not to scratch the huge shiny piece of glass.