I prefer a method which can be duplicated without expensive equipment, tons of space or electricity.
I made a make-shift green house out of clear sterlite under-the-bed boxes which I got at the local Wal-Mart.
I used paper egg cartons for the tray. The seeds that make it will grow into the egg carton, but we can just tear or cut the egg cups apart later when we re-plant the seedlings. We will re-plant the whole cup section into larger pots.
I drilled a hole in the edge of two boxes to make the top and bottom. Threaded a small bolt through the whole in the bottom box, secured it with a nut and can now set the top box on the bolts sticking out of the bottom box to complete my 'greenhouse'.
This allows me to have a deep bottom which will hold the water for the seeds and a tall top which allows plenty of room for any seedlings without fear of the top sliding off and smashing the delicate little plants.