CapitolBrand M3504-1F Borosilicate Glass Standard Grade Microscope Slides, Frosted on One End, 3" Length x 1" Width x 1mm Thick (Box of 72)
Ready to use out of the box, with no preparation or cleaning required.  Ground smooth edges provide a smooth finish to reduce the likelihood of injury.  Made from water white glass, allowing a high level of light transmission, as well as a low level of fluorescence to reduce optical interference with sample.  Frosted on one end for easier labeling.