this seems to be the only decent trackball currently on the market. i love that it is right-handed finger driven (opposed to symmetrical thumb driven). the left button placement is fine, forward and back buttons are ok, and the right button sucks (should be further from trackball and moved forward a little). but the scroll wheel should be placed closer to the trackball. it also has some other buttons that i'm still unsure about. it's a step down from the MS Trackball Explorer, but much more usable than anything else i've tried so far.
from shopping around, i actually have hope for the near future. i'm glad that MS is going to license some of its hardware IP to other vendors (e.g. tilt wheel and magnify). i'd like to see that functionality make it to a trackball. and it looks like HP and Philips are getting more aggressive in the mouse market, so maybe they will make some trackballs! because it's ridiculous how many different mice there are, but there are only a handful of average trackballs.