This parametric brick takes the popular work of http://www.thingiverse.com/thing:5699 a couple steps further, adding easy Customizer support and support for generating wings, smooth-topped tiles, DUPLO-style bricks, sloped bricks, Technic-style holes, and more.
Depending on the resolution of your printer, you may not be able to print pieces that fit exactly with standard LEGO blocks. If you do print any of these bricks, I'd be interested to know whether they fits together with other bricks, especially if you have an SLS or SLA printer.
These blocks are not strictly identical to LEGO bricks, but they should be compatible in most every way.
2016/02/14: Updated with support for double-female-sided bricks: no studs on top or bottom.
2015/01/12: Updated with support for double-sided bricks: studs on the top and bottom.
2015/01/11: Updated with support for baseplates, roadways, and better error detection.
2015/01/07: Updated with support for curved bricks.
2015/01/07: Updated with support for sloped bricks.
2015/01/06: Updated with support for DUPLO-style bricks.
2015/01/03: Updated with support for including horizontal holes to fit rods and axles, as seen in the Technic line of LEGO bricks.
2014/12/31: Updated with support for generating wings.
2014/12/30: Updated with support for hollow studs.
2014/12/30: Updated with perfect centering of knobs, posts, pins, axle holes, and reinforcements.
2014/12/30: Updated to print tiles upside-down to remove the need for reinforcement.
2014/12/30: Updated with newly accurate measurements.
2014/12/30: Updated to use a specific post wall diameter instead of an estimate based on the knob diameter.
LEGO®, the LEGO® logo, the Brick, DUPLO®, and MINDSTORMS® are trademarks of the LEGO® Group.