I have flown three times on the 737-800 that I can think of off the top of my head. All were American, and all in the main cabin. The flights were ORD-SAN twice, and LAX-ORD. I really liked the plane. I think that it's comfortable and would not hesitate to fly on it agian. As a matter of fact, I'm planning on taking a 738 ORD-SAN on Monday when I go home for Thanksgiving.
SammyK is quite right; the -900 will enter service with Alaska in 2001.
I have only flown on one NG737, with Ryanair about six weeks ago, from Turin to Stansted. That was for the purposes of an article, so I was in the jump seat for the whole flight. It was a memorable flight and the aircraft was very impressive; the cockpit is, as you know, very similar to the 777's and the clarity of the screens is a lot better than those on previous Efis types.
The landing ended with a landing at STN in heavy rain and a 30-40 knot crosswind, which was quite spectacular.
Perhaps uniquely, I will be flying on the eldest member of the 737 fleet AFTER flying on the newest! Within the next few weeks, I'll be off to Arizona, to fly on an America West 737-100. Then, I'll only have the -6/700 to go and the Alaska 739 in 2001!
I really like the images you induced in your post. My favorite 737 flight so far is a Continental 737-500 from Houston to Steamboat Springs Colorado and return. Really cool getting up and out of that mountain airport. 737-700's will be on that route for most of the winter snow skiing rush.