I recently started keeping red worms in an old 5 quart ice cream pail for all my fish (and a few crawlers for fishing bait). I had a 5 gallon bucket I kept worms in when I was a kid (yeah, I was a rather odd kid). It never dawned on me that I could keep them for my fish until a couple months ago. I spent a while thinking about things I could feed to my african butterfly fish and meandering about AA when I saw a thread about feeding earthworms to your fish.
I was feeding my ABF crickets and wax worms (they're sold as bait for ice fishing around here) for a while, but the crickets creeped me out too much. They looked too much like roaches for my liking. I'm not the stereotypical girl who freaks out about mice and various creepy-crawlies, but for some reason roaches just give me the creeps. The wax worms never lived all that long so I ended up paying for about 3 dozen worms and only using about 20. I know they're not that expensive ($2 for 3 dozen), but I wanted something that could be more self-propagating and wasn't just something that the bait shops sell only seasonally.
So a few weeks ago while I was weeding the flower beds and churning up everything so that bulbs could be replanted, I collected all of the worms I dug up. The yard has only recently become a yard (it's been a cow pasture for the last 25-30 years) and we don't use any chemicals whatsoever so the soil is extremely rich from all of the decomposed manure and there are LOTS of red worms and crawlers.
I'll probably invest in an actual worm cultivator/cooler some time in the near future. They're sold locally in the summer because of all of the people who come here and go fishing and they're never more than $8-$10 even at the expensive bait shops.