Grays is the Mecca for Nikon, although slightly pricier at times, but it's all totally kosher,
ApertureUK has a D2x in - basically a D2Xs without the built in crop mode mask in the viewfinder. D2x can have the firmware upgraded to basically become a D2Xs. That's what I've done with mine.
Those that Dave has mentioned are very trustworthy.
In terms of performance, I use two D2x bodies and love them for my magazine shooting.
Pros:
Build quality that is regarded as the best ever on a Nikon DSLR
Bright viewfinder
AF is 11-point but very fast
Built-in grip is handy and gives brilliant handling
Button layout is superb
High megapixel count so useful for A3+ outputting
Base ISO100 compared to ISO on modern bodies
Battery life is immense; expect going on 2000 shots per charge on a new EN-EL4a
Works in any weather (I have the pics to testify)
DX - good for getting more from your long lenses
Cons
Large body that people with small hands find too big
Heavy when combined with big zooms and primes
ISO noise isn't to everyone's taste above ISO 800
No built-in flash for CLS control
I used a D200 before and bought a D2X because I was a bit keen with the 'bid' button on ebay. But, when it arrived I knew I'd made the right choice; the build is supremely good, as is the handling. It's actually better than a gripped D200 or D300 because it's not as tall so button, IMO, are easier to locate without looking.
Colour rendition is brilliant, especially at ISO 100-400, and noise at these speeds is totally unnoticeable at 100 and 200, a little noticeable at 400. ISO 800 is a regular shooting ISO for me and I have no problems doing magazine covers and A3 double-page-spreads at that speed. I've even done shots at ISO 1600 (hi1) without any complaints, although you do have to get your exposure nailed at this ISO, otherwise you do start to bring out the colour noise. Mind you, I run everything through LR3 and that deals with colour noise brilliantly. ISO 3200 (hi2) is useable to get a shot, but it's not one for everyday shooting.
Majority of my stuff on flickr is shot with the D2x if you want examples
AF is superb, write speed is very, very good, and 5fps is good for action. The Crop mode gives you approximately 7mp at 8fps, so great for fast action.
WB options are good and AUTO WB is very, very reliable.
In general these cameras, like the 1D MkII for canon, are a great way to get into the (gripped) pro-body world without spending tonnes of dosh. 12mp is more than enough for most shooting and it's built to last.
I picked up my first one for £650 boxed (20,000 clicks) and my second for £750 boxes (5,000 clicks) - these days (especially on ebay) you can get them for around £550 with 20-30,000 clicks.