I am a fan of small niche single purpose tools. I was building a landing page for a web site and I wanted a screenshot of a text message.
iFake Text Message is a simple tool that handles this well. It's very iMessage-centric. It let's you customize most of the generated text message screen and adjust the bubble colors as needed. Super useful single purpose tool.
Let me know if you've got similar tools that you use. firstname.lastname@example.org. I'm looking for a tool that can transform screeenshots into something a little more interesting.