DZone just released my latest refcard today, which aims to provide developers with a useful desktop reference to UML. I think that UML is a topic that fits very neatly into the Refcard series. While most software developers have a good working knowledge of UML, sometimes I forget the small details; for example which symbol is aggregation, and which is composition? I hope that this card will help you with these types of issues.
You'll notice that that refcard is missing a reference for one type of diagram: Timing Diagrams. Originally I had written a section about these, but Refcardz have a limited space, so I dropped them. I will provide that content as a seperate article, in case anyone is interested. I'm not sure how much timing diagrams are really used in practice though. At least, I've never had a reason to use them.
When it comes to usage, I find that use case, class and sequence are the three most popular types of UML diagram in software development. Would you agree with this?