I guess I forgot to mention that the ARTICLES tab at the top of the page is a good place for basics, so I'll sneak that in.
Cuttlefish differ from octopuses in a number of ways... cuttles are more closely related to squids, and share a lot in common with them: they have two long feeding tentacles in addition to their 8 arms, they tend to swim freely in the water rather than hiding in rocks and caves like octos do, and they're rather more social with each other. They have rigid cuttlebones, so they don't change their shape as much as octos do, but they tend to have even more impressive displays than octos. They seem to show "personality" like octos do, but they "express themselves" a bit differently... they seem to prefer visual displays to touching, feeling, and manipulating as octos do. Like octos, they mostly eat saltwater crustaceans.
The only cuttles we've seen reliably recently are Sepia bandensis which stay fairly small. Several people on TONMO have tank-raised bandensis at the moment, see the "Cuttlefish Availability" thread for details.
It used to occasionally be possible to get the larger Sepia officinalis and Sepia pharonis, which require a much larger tank, but your 180 could house a small number of them. We haven't seen them in the pet trade much for the past few years, though.