I had a similar "Exception Type: EXCBADACCESS (SIGBUS) error" with a new 20" iMac. The problems typically occurred with Safari and Firefox, but I would also see errors with Mail and other apps. If I would reboot the computer, the problems tended to correct themselves, but they would often reoccur within 5-10 minutes. I installed some software at the time that the problems started, but another thing that I installed was additional RAM, replacing the 1GB default RAM with 2x2GB SoDimm (3rd party 'compatible' RAM: Patriot PSD24G667SK). The new RAM seemed to work well, and was 'operating properly' under Hardware Properties, so I concentrated on software solutions to the EXCBADACCESS (SIGBUS) conflicts. However, uninstalling/reinstalling software did not help. Finally, I re-installed the original Apple memory and the problems disappeared. I'm a victim of the WIndows XP wars, and relatively new to the Mac, so it's not clear to me if this issue was caused by bad (or incorrect) RAM, or some other software conflict with the hardware.