This stuff is fantastic. As far as I'm aware, Agfa Ultra 100 produces the most insanely saturated color images possible. It's not a great film for general use (skintones in particular are pretty unflattering), but there's no better option for creating images with deep, intense color and reasonably balanced saturation.

Here's an example: I used Ultra film in this gallery of snapshots taken with a Lomo Colorsplash camera. I used Agfa processing to develop the negs, and scanned them with an Imacon Flextight Precision II; I did basically no adjustments to the color, other than a little correction on some of the daylight shots.