I agree completely. Six Flags has gotten fantastic custom rides, and Nitro is definitely the best example. Batman: The Ride is another good example, and it went so well it got cloned as we all know.
Now that most parks have a lot of coasters and limited space, it's a great time to be a coaster enthusiast as parks have to be especially creative with their ride's aspects (layout, theme, forces, elements, etc.). And now that most manufactures can provide exactly what the park asks for due to advances in technology, the phrase, "anything is possible" becomes a reality. I think though that the best coasters are made when there are tight restrictions; the designers have to really think outside the box and something beautiful results. Whereas if they are just free to build whatever they want, they tend to think inside the box. Skyrush is the perfect example; very tight space, and it had to maneuver around Comet, and look what resulted. Intimidator 305 counts too, kinda, because KD wanted to reduce the cost by using fewer supports, so Intamin came up with the double spine, and now it is possible for coasters to push g's to the riders limit without much strain on structure or the park's wallet. Those are the only two examples I can think of right now, but there are countless more.