Cool household microscopic things?

skin flakes?

you've done the whole dog hair/cat hair/people hair thing?

dental floss - before and after

vegetable scrapings

guitar string

got any makeup? mascara brushes could be cool

comb

toothbrush - new and used

nail clippings

fly wings

drop of blood

apple skin

swab on cheek

any bug

toothbrush bristle

wipe your dogs nose on the slide

water from your fish tank ( if you have one) its FULL of bugs

buy a small microscope polarizer lens and put some sand on a slide and twirl the polarizer on the eyepiece. The colors of the sand will change under substage light and give you clues as to what kinds of minerals each grain is.
crush sugar and twirl it under substage light. MAgnificent colors.

Take things like cat piss and put it on a slide and let it dry (Careful it really stinks) and twirl it and look at the crystals of proteins.
Course you cpould also use beef broth and let it dry to a crystalline mass too.

I think you can get eyepiece polarizers from places like EDmunds or that Carolina teachers site (maybe lil K knows the site Im thinking of)

take a swab and hit the top side of your ceiling fan. Where all that sticky dust is? Yeah.

ant bodies are amazing

shower mold

Thank you all for the ideas. We had a lot of fun with the microscope over the last couple of days so I'm sure we'll be using it for further investigations.

Late to the party, but flower petals.