In your current position I would trade the two lenses you have for the EF 70-200mm f/4 L telephoto lens and then buy a Tamron AF 17-50mm f/2.8 Di II to cover the wide-to-normal zoom range.
Looking at the link to your sample photos, I see a lot of photos that appear to be taken at wider angles of view than you can get at 24mm on an APS-C body. If you give up your 18-135mm to help finance the acquisition of the EF 24-105mm f/4 L IS, you will give up a lot of your wide angle capability. The 24-105 is the lens I use the most on my Full Frame (FF) body, but for an APS-C sensor it would not be: the Tamron AF 17-50mm f/2.8 Di II was the normal zoom I used most often before I went FF. It yields an equivalent field of view (FoV) of 27-80mm on an FF body. The advantage of the 17-40 is that it is a true wide angle lens when mounted on a FF body.
In my experience, there's a big difference between the EF 17-40mm f/4 L and the EF 24-105mm f/4 L IS. I own both of them and use them on a FF body for entirely different purposes. 17mm to 24mm doesn't sound like a lot of difference, but the difference in the field of view (FoV) means about 1/3 of the area that shows up in a 17mm shot is "cropped out" of a 24mm shot. The long end is is even more disparate, as 105mm is over 2.5X longer than 40mm. In terms of image quality, most of the real world differences between the two lenses are in the corners and won't be much of an issue with your 1.6x cropped sensor 60D.
And that is where your camera body comes into the equation: How these lenses "act" on a FF body and how they "act" on an APS-C body are significantly different. I would rarely if ever recommend the 17-40 or the 24-105 to someone who doesn't plan to go Full Frame in the near future. There are equal or higher quality options in the same focal ranges for use on an APS-C body that cost much less: The Tamron 17-50mm f/2.8 bought new runs about 2/3 the price of a used Canon 17-40, for example. The Tamron 17-50mm f/2.8 I own is just as sharp as my EF 17-40mm f/4 L and is one stop faster. The extra stop really comes in handy on an APS-C body where high ISO noise is more of a concern than on FF camera with larger and more sensitive pixels. Of course the wider f/2.8 aperture also allows shallower depth of field than the f/4 lens. The best APS-C lens in this class is perhaps the EF 17-55mm f/2.8 IS, but it lists for about the same price as the EF 24-105mm f/4 L IS. The 17-55 optics are as good as or better than the 24-105, and the focal length range is better suited to an APS-C body for most shooters. On the other hand, the street price of the 24-105 has been dropping in some places as of late (a lot of unused 24-105mm lenses bought in "kits" with new 5DIII or other bodies seem to be flooding the market).
