From Craig Brown over on Better Projects:
"I propose a meme for our BA and PM bloggers.
Recall the first and last analysis model you used at work."
http://www.betterprojects.net/2009/02/meme-on-modelling.html
For me:
First: Data Flow Diagrams, having been trained on Structured Analysis a long, long time ago.
Last: a UML Activity diagram, using it to model workflow with system interaction.
This made me think of all the modeling techniques I have used in between: Entity-Relationshp Diagrams, Context Diagrams, Functional Decomposition, Action Diagramming, Affinity Analysis, Business Process Modeling, Concept/Class Diagrams, Use Cases with Diagrams, Sequence Diagrams, Business Rules... and probably more that didn't stick. I am looking forward to seeing what else comes up in the responses by other bloggers.