Codes Online  (Title 24)

BUILDING, FIRE, RESIDENTIAL CODES - The 2007 & 2010 California Building Code (Part 2), California Residential Code (Part 2.5) and the California Fire Code (Part 9) of Title 24 are available for viewing online via the following International Code Council web site link: California Codes, Title 24, Part 1, 6, 8, 10, 11 & 12 are also available for viewing and download in PDF form on this web site. 
2007 Edition 
2010 Edition (Effective Jan. 1, 2011)

MECHANICAL AND PLUMBING CODES - The 2007 & 2010 California Plumbing Code and the California Mechanical Code, are available for viewing online via the following International Association of Plumbing and Mechanical Officials web site link. The entirety of both documents are available for download and viewing in PDF form on these web sites.

2007 Edition - Mechancial & Plumbing Code
2007 California Plumbing Code,
2007 California Mechanical Code 

2010 Edition - Mechanical & Plumbing Code (Effective Jan. 1, 2011) 
2010 California Mechanical Code,
2010 California Plumbing Code

ELECTRICAL CODE - The 2010 California Electrical Code, Part 3 is available for viewing online via the following National Fire Protection Association web site link: 
2010 California Electrical Code               

PUBLISHED SUPPLEMENTS AND ERRATA
Supplements and Errata to the provisions of Title 24 are published by the code publishers.  There are three publishers of the Parts of Title 24 with recently adopted revisions.  Supplements are posted on their websites as follows:

For Parts 1, 2, 2.5, 6, 8, 9, 10, 11, and 12, (2010 Edition) the publisher is the International Code Council (ICC). 
View Supplements and Errata on the ICC website.

For Parts 4 and 5 (2010 Edition), the publisher is the International Association of Plumbing and Mechanical Officials (IAPMO). 
View Supplements and Errata on the IAPMO website.

For Part 3 (2010 Edition), the publisher is BNi Publications (BNi).
View Supplements and Errata on the BNi website.