In Shadowrun, the vulgar lingo of the streets required a number of less offensive stand-ins for common curses. Most commonly, you would "kick hoop" because that "fragger" fed you a line of "bulldrek". This has mainly been discarded in Fourth Edition in favor of more traditional forms of swearing.
If you get enough Dungeons & Dragons nerds together they will begin taking the names of fictional deities in vain. "By Vecna's dental filling!", "Pelor preserve us!", and "Moradin!" shouted at dice which stubbornly insist on rolling 1's.
Most D&D players consider 'Lolth!' (The name of an evil spider goddess) and related exclamations the worst/most serious of this variety. Players also swear 'By the Beard of Gygax!' and more recently 'By the Ghost of Gygax' or 'Great Gygax's Ghost!' (Garry Gygax was co-creator of D&D and one of the founders of the entire hobby).