An updated version of my Y-Carriage this time with Jonas KÃ¼hling's LM holder. So no more zipties.
They come in LM8UU or LM10UU variaties. Choose the one your want and remember to print the corresponding spacers.
I uses the LM10x3 version with Misumi LMU-MX10 self lubricating bearings.
More pictures here: http://goo.gl/JRg97
You will also need configuration.scad to use the SCAD files.
If you have trouble slicing the STLs cleanly, you may want to run them through netfabb.
10mm rod mount and clamp are here http://www.thingiverse.com/thing:23898
If you are printing the carriage in PLA, I would strongly suggest that you print the spacers in ABS. Especially if your HBP is close to them.
lm8x3, lm8x4, lm10x3 and lm10x4 has a smooth rod center to center distance of 98.4mm. This is what i get by measuring with a caliber. This is what i use, YMMV.
lm8x3-100, lm8x4-100, lm10x3-100 and lm10x4-100 has the default mendelmax smooth rod center distance of 100mm.
I find that the best way to get a butter smooth Y-stage is to install the Y rods into the MM body first (you need the Y rod mounts and clamps), measure the actual distance between the smooth rods, then print your Y-carriage with that exact distance.