I'll cast my interest. Just a suggestion, why not make a list of Servants that have been taken in the OP, for convenience? Saves people having to look through everyone's posts to find available servants as this gets bigger. So Far:

Saber: Claimed
Archer: Claimed
Lancer: Claimed
Rider:
Caster: Claimed
Assassin:
Berserker: Claimed

I'll take Assassin I guess? I should be able to find something interesting.