I put the sliced onions (vidalia or candy) with a small splash of olive oil into a skillet on high heat (no salt) and cook them for 10-15 minutes, stirring them around every couple of minutes. They always come out perfectly. I don't know why people are saying 30 to 45 minutes or hours in a slow cooker, or adding water, butter or sugar or whatever - all unnecessary and time consuming. Adding water in particular seems like the worst possible thing you could do as it's just going to steam them, which isn't what you want at all (adding salt essentially does the same thing by drawing water out of the onions).

I also don't add garlic, as garlic will just burn under the same conditions that caramelize the onions.