DPReview is probably the site to see.

http://www.dpreview....oducts/nikon/slrs

The different model numbers seem to mainly correspond to different calendar years of introduction.

Prices are mainly going to be driven by the sensor size and the electronics. Smaller sensors are cheaper, but noisier (fewer electrons per picture element). For a full-frame sensor, you're looking at thousands (e.g. $3700 for a D3 body). For a D5100 (2011 camera) with an APS-C sensor, you're looking at $800 for a body. DPReview's take on the 5100 is here - http://www.dpreview....nd5100/page22.asp The D7000 gets a higher score, but costs almost $400 more for the body - http://www.dpreview....nd7000/page22.asp

HTH a little. Best of luck!

Cheers,
Scott.

(Helps when friends want to know similar, and I pay little attention to cameras, of late.)

Love the literate, concise and accurate descriptions--just as I would wish for, if 'deciding'.
Obviously he has a good editor and I'd guess.. might once have been an English Major? :-0
His multitasking is superb--apparently he does keep-in-cache all the minute differences, 'tested' by self and reported--at some relevant phrase-- as to significance: you can't 'distill' in a more granular way than that, IMO.

Keeper for REF.

(A while back I acquired a Canon S-2, after seeing Squeak (!) pix taken by neighbor's--the rock-steady results of an authentic 15x optical zoom, with functioning stab. ctrl.)
Except I got mine near pristine for a pittance, off eBay: given the artificial obsolescence engendered by NewModel-itis everywhere.)
I even got a copy of a rather complete after-market manual about this specific model, courtesy of L.

Mine seems not (yet?) to suffer from a particular blight / for which also there is an iFixit-style how-to, for those who are Not fumble-fingered
and who comprehend the torque requirements of jeweler-size screws, and such. One would wish for 'smaller' except when actually Using this right-sized for human hands object.
(I fail to grok-at-all how people 'use' the credit-sized gadgets while actually composing any difficult shot.)

Ah well, back to sleep re. the brilliant future of transistors+cameras: as shall never make any cluless One, Ansel Adams II.

Welcome to IWETHEY!