Links
On common-centroid layouts:
http://www.ece.utah.edu/~harrison/ece5720/Common_Centroid.pdf
Generally on analog design:
http://www.ewh.ieee.org/r6/scv/ssc/Allen_Practice_Analog.pdf
The BSIM MOSFET modeling website:
bsim4 www-device.eecs.berkeley.edu/~bsim3/bsim4.html
An article on process parameter variations:
J. Lao et al., "An IC Manufacturing Yield Model Considering Intra-Die Variations", in Proceedings of the 2006 Annual ACM IEEE Design Automation Conference (DAC). http://portal.acm.org/ft_gateway.cfm?id=1147100&type=pdf