This is an image from a terrain renderer I've worked on sporadically over the last several months. Highlights include...
Reduced triangle counts using standard view frustum culling and
geomipmapping implemented basically as Willem de Boer described here. To link patches of different levels I used flanges instead of altering the index buffers though.
I also implemented the procedural clouds technique described by Kim Pallister in GPG2 and plopped the texture on something that resembles a skydome. Actually, im not sure how close i got to exactly what was described there, but I think it turned out pretty well =).
Grand canyon data was pilfered from here. I didn't use the whole thing, just grabbed a piece that looked interesting.
Binaries and Source can be found at http://www.bol.ucla.edu/~mdegeorg/TREND.zip. And I have to give a shoutout to the regulars in #flipcode. Without them, this would have taken twice as long.