Hi Celstar, welcome to the forum!
I have a D2x, and the lens I use the most with it on land is the 17-55 DX. It is the best quality lens I've ever used, very sharp, amazingly fast, great color, but it is expensive and heavy. Underwater I use the 10.5 and 16 fisheyes for wide angle and the 60 and 105 for macro. Unfortunately, there is no one-lens-does-all solution.
As for housings, there are many great options. I have a Subal and really like it. When I bought it six months ago, Subal was the only one that was producing housings for the D2x, but I think that if I was buying it now I would probably choose Subal again. It is relatively light and compact (important for me, as I travel a lot), but it is expensive. There has been some good feedback on the Seacam and Nexus. Aquatica is also shipping a D2x housing now, and it is the cheaper of all, but there is no formal review out yet. Take a look at these links for housing reviews:
Subal:
http://wetpixel.com/i.php/full/nikon-d2x-a...bal-nd2-review/Nexus:
http://wetpixel.com/i.php/full/nikon-d2x-a...housing-review/Seacam:
http://wetpixel.com/i.php/full/seacam-niko...ort-and-review/And some first impressions on the Aquatica:
http://wetpixel.com/forums/index.php?showtopic=10320You may find more information by searching the forums, there was a lot of discussion about D2x housings lately. I hope this helps,
Luiz