I got those too...not sure if they are mites or whatever. You could try washing them off with a stream of water or use a mixture of soapy water (some say use Dawn...others say Ivory). I had a bottle of Safer insecticidal soap that I used...they all look dead now and I washed the plant down good the other morning with water.

Perhaps the cast skins of aphids.

If they are dead -- sort of skeletal and not moving if you touch them, they are probably moulted aphid skins -- in which case you have aphids and the Safer soap routine will get rid of them.

If they have wings and fly away when you poke them, they are probably white flies. Safer soap will help, but so will looking on the underside of the leaves of your plants -- if you see small rings of white powder, that's where white flies are laying their eggs. I gently rub those white rings and any little bug things around them to squish them -- that way you kill the larval and egg stages.

If you have a lot of white flies, putting a yellow sticky card next to your plants may help -- White flies are apparently very attracted to the color yellow and most garden and hardware stores sell sticky cards for them: they are yellow cards, some 4X7" in size covered in a very very sticky stuff that y;ou hang or put on a stick near the plants you want to protect. The adult white flies fly over to the color yellow and try to land and then get stuck on the sticky stuff.

I have one card between each of my tomato plants and between those and gently rubbing off any white circles I see on the plants, I can keep the white flies in check.