Random thought I had since I've been on a Touhou binge lately (the amount of remixes, including actual voiced songs, of game themes out there is amazing): Touhou classes!
Archer: Yukari, obviously. Not because shooting things is her shtick (it's everyone's shtick), but because she's broken. NP: Something GoB-esque, perhaps a train rushing out of a portal straight at someone.
Assassin: The three mischievous fairies who can become invisible and soundless and detect others, maybe? I dunno if three peple can become one servant (perhaps they can if they are always together in their story?), or if they're even significant enough. NP: No idea.
Berserker: Yuugi or Suika, probably, since they're oni and therefore freakishly strong. Both also have borked powers. Their NPs would probably be cups of sake or something.
Caster: Most likely Marisa or Alice, since they're specifically witches.
Lancer: Remilia, perhaps, if only because she has Gungnir.
Rider: Youmu doesn't really ride anything, per se (except perhaps Yuyuko in certain doujins...), but she does have the speed.
Saber: No idea... not many characters actually use a sword. There's some Tengu Catgirl chick, but I favor Flandre (who has Leavatein) because I'm into psycho girls.
My list
Archer: I'd go with Yukari only because nobody else really fits more than the others, and she fits the two Archers we know. In a danmaku game, pretty much EVERYONE qualifies.
Assassin: No freakin clue, Sakuya's abilities would fit the theming though.
Berserker: Flandre would be ideal here. Nobody goes berserk like she does. Suika maybe if she goes on a drunken rampage.
Caster: Patchouli, come on, pick the single best mage in the game! When shes not sick with something
Lancer: Only one spear wielder, so Remilia is it.
Rider: Reimu started out by riding this flying turtle, so yeah.
Saber: Youmu's got the blades.
Now, how about a cross series Servant assignment? One Servant per source:
Archer: Takamachi Nanoha(Nanoha)
Assassin: Nanaya Shiki(Tsukihime)
Berserker: Uzumaki Naruto(Naruto)
Caster: Yuki Nagato(Haruhi)
Lancer: Negi Springfield(Negima), hey, Titanslayer counts right?
Rider: Lelouch Lamperough(Code Geass)
Saber: Cloud Strife(Final Fantasy)
Whats yours?