Here is a link to a great piece at Smithsonian regarding the political history of the SO2 trading program. My favorite part is G.H.W. Bush pushing for a bigger reduction (i.e. a tighter cap) because everyone understands that double-digits are important.
Here's a short blog post at the WP regarding Europe's program and a more recent post.
Here is a short piece from WRI regarding cap-and-trade in California.
The San Jose Mercury News has an informative piece on the nuts and bolts of California's system.