"You Rock!" theme: party favors are pet rocks, music is rock-n-roll, tables are named Quartz or Obsidian and such. "You're Golden": everything possible is gold-colored, music is "golden oldies". "You're Precious": faux gemstones everywhere.
A fun theme is a hawaiian theme. You can give everyone lays. Serve tropical drinks. Play hawaiian music or ocean sounds. Another option is to choose a decade, such as the 60's and use that as the theme.
Relate the theme to the accomplishment. For example, a spa party, with chair massages following work on a hectic, stressful project. A superhero party is fun, especially related theme gifts.
Plan your party around the chant, "2, 4, 6, 8, who do we appreciate?" Make sure that everything reflects one of those numbers -- 4 kinds of soda, for example.
