When I was first exposed to japanese language, there were three pronouns I learnt - 私、僕、and おれ。 But I've seen more pronouns and am not sure when they would be used - わたくし、わっち、わがはい、うち、おれさま、and みずから(?) If anyone could help me with these I'd be grateful!!
I can only answer for おれさま. This is a very pretentious way of saying "I". You're putting yourself above the interlocutor. If you watch the famous drama "Hana Yori Dango", one of the main character is a pretentious descendant of a rich family. He uses this way of talking when interacting with his girl friend which is poor, since he thinks poor people are worthless.