Since this was bumped:

So, I've made a start on re-organising things slightly. I've added Sir Ementaler's tiles to the main image, and added a bunch of red X tiles to mark the empty areas more clearly. Also, I removed Violet's cave tiles, as they were rather messy from a usage perspective and Sir Ementaler's alternative seems to be somewhat simpler.
Lastly, I removed the background aqueduct things from the main image. We can still use them later if they get revised, but for the time being they still don't tile so they have been removed.
Oh, and the thing has been reduced to the right colour depth again.
So now we have about 380 tiles. A few less, considering the blanks in there. Either way, we have a good base to work from, and I think we need to focus on eyecandy now. If anybody has any tiles they think would fit, go ahead and submit them. Don't worry about colour depth, I'll personally reduce them to whatever is needed if they are drawn in 24-bit rather than 8-bit.