Number of units: 6
Sonobe units by Dave Mitchell: Part I and Part II. To assemble the units, Instructions for Assembly with Sonobe units (PDF) — this is a free chapter from Meenakshi Mukerji's book: Marvelous Modular Origami (2007, 92 pages). To assemble many more models using Sonobe units, check out this article.
Comments: Easy to assemble. Great for beginners.