Other
Science Spot: Microscope Mania [Pdf]
This is a lab station lesson plan on microscopes (7th grade). There are several supplemental documents available to accompany this lab at: http://sciencespot.net/Pages/classbio.html - Click on Microscope Mania.
NASA
Microbes @ Nasa: Science Lesson Plan: Day One Microscope Activity [Pdf]
A middle school experiment on the cell structure of cyanobacteria.
Huntington Library
Huntington Library: Garden Lesson Plans: Investigation: Pollen Collection [Pdf]
After learning about what pollen is, its health effects, as well as how it benefits humans, middle schoolers take part in a lab activity. For this, they collect schoolyard pollen on slides, stain it, and then examine it under a microscope.