There have been a few situations where “hearting” a post isn’t the exact connotation I wish to convey, for example notifying a user that I’ve read their reply, or "+1"ing an idea. Custom emoticons is useful in allowing these ideas.
I think GitHub’s subset of emoticons is fine (+1, -1, laugh, hooray, confused, rocket and eyes), however the best plugin for Discourse I’ve found is Retort:
Relevant discussion: Is there a downvote operation?