In general, substitution ciphers are those in which characters from the plaintext are simply substituted (replaced in a specific manner) with another set of characters, which results in the ciphertext.
A list of Substitution ciphers
The Homophonic Substitution cipher is a substitution cipher in which single plaintext letters can be replaced by any of several different ciphertext letters. They are generally much more difficult to break than standard substitution ciphers.
Base64 isn't really a cipher, but I see it used all the time for "enciphering" text, so it gets an honorary mention.