Next Lens for my Nikon D90?

I'm thinking of getting the Tokina 11-16 f2.8 for my Nikon D90.
or should I be considering the Tokina 12-24 f4? Or any other type of lens like the sigma 10-20mm f4-5.6?

At the moment, I have:

Sigma 70-200mm f2.8
Nikkor 24-85mm f/2.8-4D IF
Nikkor 50mm 1.4

I'm really picky about my lenses so I really don't want to invest in something I won't be able to use constantly. A lot of my friends have been telling me to get the Nikkor 24-80 f2.8 but I'm still a student and it's unbelievably expensive. I would really like a wide angle lens to shoot group shots inside crowded spaces as well as buildings when i'm in close range.

Please leave a quick review about the tokina 11-16 for anyone who owns it.

I don't own the 11-16, have shot it and like the 24-70 it's one of those lenses that are difficult to hand back to the owner. The sigma is perfectly fine and serviceable but it doesn't handle nearly as nice as the tokina. The 12-24 is pretty good but the 11-16 gets you a stop more and the build of the AT-X pro series which is lovely.

I have the Tokina 11-16 on a D90. If you want a super-wide angle lens, this is the one. It is better than the Nikon 10-24, as the Tokina is a pro level lens; fast f/2.8, and built like a tank.

I use it mostly to take photos of interiors of cruise ships. My wife and I have taken to cruising a lot lately, and this lens, with it's fast aperture and field-of-view will give me nice full interior shots.

It would also be good for interiors of museums and other buildings.

And since it is a superwide, although the f/2.8 is not required for landscapes, it makes for an excellent landscape lens as well.

One indicator that the lens is good… Dealers have a hard time keeping them in stock.

I think it is one of the best lenses Tokina has ever made.

I would opt for the 11-16 vs 12-24 for the low light capability. The difference between 16mm and 24mm at the telephoto end is not significant, and you do not need to cover every millimeter anyway.

Since the rest of your lenses are fast - more or less - you would probably like the 11-16.

I use the Tokina 11-16 and love it dearly.

The limited zoom range isn't much of an issue, one uses it at the 11mm mark most of the time anyway. The f/2.8 can be very useful for handheld indoor shooting, making it perfectly usable when stopped down to f/4.

Here is such a sample shot, taken handheld at 11mm, 1/30s, f/4, ISO 320.

Take a look at the nice corner sharpness. Every mosaic tile is clearly visible in the lower corners.

It's only real downside are relatively strong chromatic aberrations, but the D90 fixes the lateral ones automatically when you shoot JPG, and when you shoot RAW they can be fixed in Lightroom.

Edit:
That lens also has a dirty little secret: At 15-16mm it works on full frame without vignetting.