Home made with some agar agar and wort. It works pretty good.
I have also split a White labs vial into 15 empty vial with wort and let the ferment for a few days with the caps loose, then stored in the fridge. I need to make a starter each time to get the yeast count up. They have been in the fridge for about a month now and still look good.
You can also store in the fridge with distilled water.