Canon 50d noob

Fortunately you don't even need an L-series lens...

Morro Bay Harbor
EF 20mm f2.8 lens at f5.6, B+W Kaesemann C-Pol, EOS 50D at ISO 200, 1/400.

I know you can't see the detail very well on the Internet and at this size, but this was one of several thousand shots I took on a trip in the Fall of 2009. When I got home and was finally reviewing things on a "real" monitor, I thought I'd shot this with my 5D MKII at first, then noticed the EXIF that I'd used one of my 50Ds. See the black yacht anchored way out in the harbor? In the 16x20 print you can see the Jolly Roger flag flying on it. Rigging lines are clearly visible on all the boats except the most distant toward the right edge, where there's always somewhat less resolution with any camera.

It's good you don't need an L-series, because none exists that's particularly wide on a crop sensor camera... at least not at a sensible price. The 14/2.8L II sells for $2250 and loses a lot of it's "wideness" on a crop camera. The 16-35/2.8L II sells for $1700 and is even less wide. The 17-40/4L is the most affordable, but not particularly wide either.

Fortunately, there are a number of UWA lenses specifically made for crop cameras, that you can choose among for between $500 and $850 new, a little less used. Note that no "crop specific" lens from Canon will ever be an L-series, no matter how good the lens is. The reason is that part of Canon's definition of an L-series is that it must be compatible with all EOS cameras past, present and future. EF-S lenses are only usable on the 1.6X/APS-C crop cameras, can't even be fitted to 1.3X/APS-H, full frame or film Canon.... so can never qualify as "L's", under the company's own definition of the series.

All other considerations aside, for the particular shot you linked the Canon 10-22 would be my first choice for one reason... It's very resistant to flare and there are a lot of strong, specular lights in that night image. Tokina 11-16 and 12-24 are also excellent, but you'd start to see some flare in them with this particular type of photo. Sigma 10-20 would show even worse flare (at least the version I tested some time ago, there is a newer version now I haven't tried). I don't know about the Tamron 10-24 or Sigma 8-16... Haven't tried them, but really can't imagine them being as being as flare resistant than the Canon 10-22.

Personally I use the Tokina 12-24. I just couldn't justify the $350 or so extra cost of the Canon, for the little bit of occasional flare I have to deal with using the 12-24, or for the difference between 10mm and 12mm (two steps backwards). Plus IMO the Tokina is a lot more "L-like" than the mid-grade built Canon.