"ISO - Everybody knows the D90 does better in low light. But what about direct sunlight? The D200 shoots natively at ISO 100. The D90 starts at ISO 200. This matters if you are trying to use flash to tame your ambient light. It's like having twice the flash sync speed. "
I think Willis point is largely missed by A LOT of people, having native ISO is a great advantage of the CCD chip. . .heck, the CCD sucks at high iso's unless you REALLY work with the engineering behind it (let's see what the D3k does, and take a look at some of the high-ISO shots from a 10.2 mp CCD sensor on the Ricoh GD3 that was just released). . .
this topic has been hashed before many times, and as a recent D200 owner who was debating between the D90, it came down to the following:
1. If you have pro-inclinations, the D200's layout is VERY similar to the D300/D700/D3 bodies, which means the learning curve you put in NOW will pay HUGE dividends later; this mattered to me, as I started a photography company and knew the D200 was a just a steal at $599. Only comes with A, S, P, and M; the D90's "scene" dials lend itself more easily to a beginner.
2. Size and sealing; the D200 is just better built, nicely laid out, and its shutter is built to last a lifetime; the D90 felt smaller and toy-like in MY hands (you should see for yourself).
3. quicker native fps; I know 4.5 and 5fps is minimal, but to me, I needed every extra oomph I could get for the event photography I do (emotions are a split second thing, so if I capture something timeless, more bank for me)
CONS of D200 vs. D90:
1. view finder sucks compared to the D200, the D90 is just bright and brilliant (not as nice as a D300, but still nice).
2. CF vs. SD - I had to buy 2 CF cards when I bought the D200, but CF is standard fare for pro bodies, so better to invest now. . .
3. above ISO 640-800 sucks compared to D90. this is the CMOS vs. CCD debate here.
4. Gen 1 processor vs. Gen 2 - so things like Active d lighting, and other in camera enhancing tools are lacking; however, if you use a software suite like DxO, you will have more lenses covered under the D200 than D90, which worked well in my favor (so maybe not a con, not sure?!)
5. HEAVY!! You'll feel it, the D90 is easier for hikes and all day romp's. . .the D200 gets a little old after about 6 hours. . . .in the field, my adrenaline is pumping so I don't feel it (esp at a wedding), BUT, the next day my old ass is sore. . .
Neither are a bad choice, so it's up to the OP to go and test them out, don't trust our e-opinions!