I finally saw The Hobbit (part one, my goodness!), and aside from enjoying it I also spent some time racking my brains over where I knew those actors from.
My conclusions:

That main hobbit: the dude from Sherlock, but not the main dude. Also Arthur Dent one time. Old version: in goddamn everything.
Pointy-hat man: Bad X Man
Main dwarf on quest (tall) (royal?): mill owner in that Industrial Revolution romantic miniseries Joan said I should watch. Also the Vicar of Dibley’s dream man.
Sexy Dwarf #2: The vampire from that UK show where the werewolf had stickey-outey ears and the ghost always wore that nice belted cardigan.
Main Elf: bad dude from Matrix, good dude from Priscilla.
White-hair wizard: bad dude in everything, often a vampire.
Poop-stained wizard: time travel guy with question-mark umbrella.
Main fat goblin: Dame Edna, cast against type!
Elf that welcomed everybody to elf town: Flight of the Conchords guy!!!!

Everyone else did a guest role on Xena: Warrior Princess because, you know, New Zealand.