+1 for 17 TS-E + 1.4 TC
This is an amazingly versatile lens despite the wide field of view due to the almost complete lack of distortion.
As mentioned it is not quite as sharp as the 24 but from an owner of the 17 who is also a pixel peaper, I can tell you this lenses will satisfy most anyone's need for sharpness, especially in terms of corner performance.
I also love that I can get really close to my subject if desire / required. Great for indoor work and if you really want the 24mm just add the TC for only a marginal IQ penalty. But I can promise you will love the 17mm FOV!
Oh, and BTW, As you will see from the sample below you can definitly use ND / CPL / Grads on this lens. Fotodiox makes a great filter system I have been using for a few months now that allows for both Screw on filters, ie CPL / ND, and Grads. It's called the Wonderpana and it is built like a tank. Very high quality materials and it is made specifically for the 17 TS-E. I actually never take it off the lens, as it also protects the front element.