There was a diary earlier today called "List of Mormon-Run Companies" which appears to have been deleted (for good reason) after being on the rec list. We really should not be boycotting companies just because a Mormon (who may or may not be against Prop 8) owns or is part-owner of a company. That would be discrimination at an extreme. That would be as bad as if we were to campaign against Democratic Senatorial candidate Tom Udall in New Mexico (who I'm very glad won)--or if we were to campaign for Merkley in Oregon just because Smith is a Mormon (versus because Smith is a lousy Senator). However, there's a different way to take action, if one chooses to go after the church...go after companies actually owned by the church itself. More below...
Here's the list of Mormon-owned companies on Wikipedia. This may not be complete, but several of these are well-known, especially Bonneville Broadcasting, which has radio stations in some big markets (including 100.3 the Sound in LA, which I can get in my car here in the northern part of San Diego).
Beneficial Financial Group
Bonneville International Corporation (owns a lot of radio stations--including 100.3 the Sound in LA!)
Deseret Morning News
Temple Square Hospitality
Here's the source...
Deseret Management Corporation is run by top officials in the Mormon church, including the First Presidency.
Again, if one must go after the church because of Prop 8, go directly to the source--don't harm LDS members themselves (who, again, may or may not be for Prop 8--and even if they are, they may not have made an effort to get Prop 8 passed)!