Las Colinas has some nice paved trails that are great for rollerblading or biking. There are also wooded trails for running off the hard cement. The trails go pretty far to the north (about 3.5 miles one-way), and 1.5 miles south.
I plan on rollerblading, but feel free to bring your bike instead if you prefer. Runners are welcome too, but may not be able to keep up with the ones on wheels.
If you arrive late and we're already gone, take off to the North, because that's the way we'll be headed!
Here's the link for parking and a good view of the area: http://maps.google.com/maps?q=park&hl=en&ll=32.88074,-96.930184&spn=0.011136,0.019205&sll=32.879407,-96.930453&sspn=0.005568,0.009602&vpsrc=6&t=h&radius=0.33&hq=park&z=16&iwloc=A