I just bought a D300 and an 18-200mm VR lens a week ago. Where to buy?
Well, that really depends on who you are, and what your priorities are
Say you are an experienced photographer, who knows his/her way around advanced gear. If so, you already have looked through the various boards and have a list ready of what you want to buy, because many of the best deals are "bundles". If you are not interested in some part of the bundle, you'll look at different deals - and that may make a deal "great" or "poor".
Do you already have lenses? If not, you'll definitely need to buy lenses at some point. Are you comfortable with buying a lens immediately, or will that break the bank and you have to wait on that? For example, I read up on the D300 and I knew I didn't want the kit lens - originally, I was going to buy the Nikkor 24-70mm. However, that lens has been out of stock for long stretches, so I can't buy it so easily. Meanwhile I wasn't planning on buying the 18-200mm VR, because I didn't think it was worth the listed price of $700. Then, Nikon started running a promotion: a $300 dollar instant rebate on the D300 + 18-200mm VR combo. At that price, the 18-200mm VR suddenly started being interesting. I decided to go for the deal. If you are not interested in the 18-200mm VR, and only want the body, well, this deal is not for you. In any case, various merchants started to compete for this deal. The best I've seen was the short-lived (a few hours) deal through Adray Camera at $2,049.00 with free shipping and no tax (I'm in CA, Adray is in MI, and this was an internet purchase). I got it, and was very pleased. The camera is brand new, and has the NX Capture software included.
There are many variations on this bundle deal. Some charge a slightly higher price (f.ex. $2200), but include additional goodies, such as CF cards. You must evaluate if you need those "goodies". The very best I've ever seen was a bundle by Cameta Camera "buy it now" on Ebay - it was an even better deal than mine, because even though it was $2,099.00 it included amazing additional accessories (optional grip plus more!). That was truly unrivaled - but again, depending on if you need what the bundle offers.
There are also the deals that combine coupons - such as Best Buy 10% off with the $300 rebate. Not all BB honor the combo of 10% off and the $300 rebate (technically, they don't have to), but that brings it to something like $2,015.00 - BUT you pretty much can't avoid tax in this situation, which makes this more expensive. The best coupons deal I've seen was a Dell deal with stacking coupons and the $300 rebate into something pretty spectacular, but this is not practical for most people, as you usually have had to accumulate the coupons for quite a while.
The $300 rebate on the bundle runs through 05/11/08, so you have some time, except for one fly in the ointment. Nikon has been providing the NX Capture software for free (a $100) value with the purchase of a D300 - but this was a temporary promotion, which expired with the last produced D300 at the end of March. This means, that when the stock of cameras produced in March is cleared from the channel, you will not get the NX Capture software. The longer you wait, the bigger the odds that you'll miss that.
If you don't want to buy the 18-200mm VR lens, it may still be a great deal to go with the bundle - since you can re-sell the brand new unopened lens for a lot more, your cost of just the body can be substantially lower than anywhere if you were to buy just the body itself. More exotic deals are also possible. Say, you go in on a deal with someone: they need the body only, you the lens only or vice versa - buy the deal, and split it for mutual benefit.
Buying online can be tricky. Stay away from vendors who have bad ratings on resellerratings.com, or have no ratings. Also, be very careful that you buy from an authorized Nikon vendor. If you don't, odds are you'll be buying a gray market camera - this means it's not a camera that's been approved for distribution in the U.S.A. and you may have trouble getting your warranty honored should something go wrong. So, buy the U.S.A. version, not the "imported" version!
I prefer to buy online, not just because I can save on tax (technically, you're supposed to report the purchase on your state tax filings, but there are legal ways around it), but because I actually trust specific online vendors MORE than local photo shops. Let me tell you why: my trusted online vendors will always send me NEW product. Meanwhile it is very common for local B&M photo shops to sell you a demo model without alerting you to the fact that it's not new.
Customer service: online vs local. If you are an informed consumer, you already scoured the boards and made a list for yourself of all the commonly reported flaws in your camera model and the lens you intend to purchase. When choosing a vendor, you are already aware of their returns policy. Therefore, the moment the bundle arrives at your doorstep, you inspect it carefully, and you run tests against your list of flaws and test the unit generally. If you find a flaw - send it back in and exchange for a new one (check first to see if there's a re-stocking fee, this you should have done before even buying). There's usually a 2-week or so term for returns, so that's why make sure you are in a position to perform the checks immediately. So, if you are an informed customer, buying online should give you no worse customer service than buying locally - always provided you've checked out your vendor ahead of time.
Online vendors I've had good dealings with: B&H, Adorama, Cameta, Adray Camera, Buydig, Amazon, Ace Photo Digital, Dell. This list is based only on MY experiences with photo equipment, so it's not exhaustive. Make sure you check to see if a vendor charges taxes (usually if they have a physical presence in your state, they will charge tax). And make sure you factor in any deal you see the cost of tax and shipping (was $0 for me).
When you get your camera + lens, remember, Nikon offers extended warranties - it's your call if you want this with the D300, but you have up to a year from the date of purchase to buy it. Not so with the free extended (beyond the first year) warranty on lenses - 5 years - this you must send in to Nikon within the first 10 day from the day of purchase, so don't let this fall through your fingers.
Hope this helped!