Here's a conundrum - what Nikon digital body do you buy for $500? There's quite a range now from older pro models to brand new consumer models, and mid range models in between. Depending on your needs, any one of these could be suitable. So let's take a look.
Pro - Nikon D2X
This was a $6000 camera when it came out in 2004, and was state of the art. For its time, the colour rendition was excellent. It also has a full metal weather proof / dust proof pro body with huge batteries that last 1,000s of shots and a shutter rated for more than 200,000 cycles. It meters with manual focus lenses and auto focus with AF-D type lenses. However image quality at high ISO is nowhere near as good as modern sensors, and while its large size lets you look like a pro, the camera's weight does get to be an annoyance.
My user experience: My D2X was a high mileage example and it had a few problems, including a sticky trigger, circuit board malfunction and peeling grips. At ISO 800 and above the noise levels were not acceptable, and no in built flash was a draw back for me. The 2.5" screen is also not as nice as the later 3" screen.
Summary: Nikon pro durability with older levels of high ISO performance.
|Nikon D2X with Tamron 90mm macro|
Semi-pro - Nikon D300
The Nikon D300 is a good camera. Full featured, the 12MP sensor was a big upgrade on the D2X, especially above ISO 800. It also metered with manual focus lenses and had the AF screw drive for AF-D lenses. The later D300s has video and is about $200 more on the used market.
Summary: Great balance of pro features and image quality
|Nikon D2X with Nikon 135mm f2 Ai-s|
Mid level Consumer #1 - Nikon D90
The D90 is more consumer focused than D300, though it has the same sensor. It deletes the metal body and features like manual focus lens metering, PC sync plugs and a few other bits; though it does have 720p video. It is also lighter and smaller. You can get a D90 for $100 - $150 less than a D300, so you could pick up a battery pack or a cheaper lens within the $500 budget.
My user experience: The D90 has been a good camera for me. It is nice and light for travelling and the high ISO performance is good. The flexibility to use AF-D lenses is also a very welcome feature.
Summary: A consumer D300
|Lunenburg NS - Nikon D90 with Sigma 10-20mm|
Mid level Consumer #2 - Nikon D5100
The D5100 is pure consumer camera, but it does have some very good features. Chief amongst these is the excellent 16MP sensor, which is excellent at ISO 3,200 and still very good at ISO 6,400. It also features 1080p video and a cool swivelling screen. However the body, while light, feels cheap and nasty, and you would definitely not want to drop one. There is no screw drive, so AF-D lenses want auto focus, and neither will it meter with manual focus lenses.
My user experience: I haven't owned one, but my brother in law does, so I have had some time with one. The camera had excellent image quality, but I felt more at home when he handed back my D90.
Summary: Fabulous image quality, but you'll get sick of it quickly
Wildcard - Kodak DCS Pro SLR/n Full Frame
Based on a Nikon F80, but fitted with a Kodak Full Frame sensor, this camera series was launched a full 4 years earlier than the Nikon D3. However, whereas the D3 is an excellent camera, the DCS Pro has behind even the Nikon DX D-SLRs of the time in terms of speed, ISO performance, flexibility and image quality. In fact it drove many users crazy. However, if you did manage to get it right, the sensor had that classic look you can only get with full frame.
Summary: Will likely drive you crazy
|Halifax NS - Nikon D90 with Nikon 18-200mm|
Conclusion: Like everything it depends on your needs and usage requirements, but for me the D300 is the one I would buy.