What are the lesser known but useful data structures?

There are some data structures around that are really useful but are unknown to most programmers. Which ones are they? Everybody knows about linked lists, binary trees, and hashes, but what about Skip lists and Bloom filters for example. I would like to know more data structures that are not so common, but are worth knowing because they rely on great ideas and enrich a programmer's tool box. PS: I

[amagitakayosi]

おもしろ

[natsutan]

@finalfusion が好きそう

[rindai87]

あまり知られていないけどイケてるデータ構造は？後で読もう

[mooz]

必須

[mad-p]

クールなデータ構造集まれ