Nikon Wide-Angle Lens?

I have a couple of Nikon DSLRs (not full frame). At the moment, I only have the standard lens and the Nikon 18-200mm VR 3.5-5.6G lens and I'd really like a wide-angle lens such as the 8mm and above ones. I have a really low budget so nothing over $400 so it's obviously been hard finding the best lens. Any suggestions or lens you've previously owned and what you would recommend getting. It doesn't HAVE to be under $400 as I'm open to all the recommendations but I'd like it around that price range.

I have a Sigma 10-20 f/4-5.6 that gives excellent results.
http://www.amazon.com/...0007U00XK/

Not quite 8mm but 10mm is pretty wide and you get $1 change from your $400 ;-)

If you want to go 8mm - and don't want it to be a fisheye, the Sigma 8-16mm is about your only choice. It is a bit more expensive though, around $650.

http://www.amazon.com/...003G28AZG/

I have this lens… If you want wide, go with the Sigma:

http://www.althephoto.com/lenses/ultrawide.php

Just to give you a choice, Tamron AF 10-24mm.
http://www.amazon.com/...001G7PIBC/

And only $20 over your budget.

Couple of suggestions for you;
- the Sigma 10-20mm f4-5.6. I have this on my crop sensor Nikons & it's a great lens
- the Tokina 11-16mm f2.8 - gets rave reviews & the 2.8 aperture might be appealing

if you want wider than those, the 8mm Samyang rectilinear lens is superb value for money (I don't have one but a mate does & I'm impressed with the shots he gets.