Alright, the following is a list I put together to illustrate what people I could envision as Servants. The names in the bracers is what I thought up as possible Noble Phantasms or how they could fight). Some could be summoned as another class as well, like, say, Leonidas or Musashi could also be Sabers, for example.
Siegfried (Sword Gram)
Hyppolyta (Belt of Ares)
Alexander the Great
Icarus (Wings of Icarus)
Cleopatra (including a horse-carriage)
Headless Horseman, Dullahan
Vlad the Impaler (Necromancer+Blood)
Prometheus (God's fire)
Laertes (from Hamlet)
I'd like to note here that I would really much like to play Jeanne d'Arc as a Saber.
Incidentally though, going by the rules of summoning, you could pretty much summon ANY fictional character. Meaning you could probably summon Batman or Superman to fight for you. But then again, that would be kind of silly, right?