Low and slow is the only way to go, I'm afraid.
You can add some broth and simmer them down (as opposed to just cooking them in oil) but make sure you add little enough that it will all evaporate...
Don't want to be pouring off flavor.
cooking.stackexchange.com/users/218/Satanicpuppy
In addition to what everyone else has said, you may want to add some salt as the onions caramelize.
The salt will help draw out the sugars, and allow them to caramelize more.
Some techniques I've seen also suggest a little sugar to help the caramelizing process...
but personally I think that's cheating.
That's up to you though.
cooking.stackexchange.com/users/260/Nick
I think you've answered your own question.
Low & slow, with constant stiring.
To hot & fast will burn the sugars you are attempting to bring out of the onion.
I don't believe there are alternatives to doing this.
But maybe someone will correct me.
cooking.stackexchange.com/users/20/Tree77
In a very low effort way you can do it with a crock pot .
Put in 2-4oz of butter depening on crock pot size and as many onions as the crock pot will hold.
Set it on low.
Come back
8 hrs later.
cooking.stackexchange.com/users/2045/Laura Thomas
I generally use butter, EarthBalance, or extra virgin olive oil, and lots of time.
If I'm in a rush I will sometimes turn the heat up a little, but the that nearly always causes an inconsistent or lower quality result.
Also I find it helpful to separate them onions early in the process.
Generally we slice them into rings before cooking.
I separate the disks as I place them in the pan.
I've found that while this increases the space they require for cooking, it greatly improves the quality of the results (again supports even cooking).
cooking.stackexchange.com/users/161/acrosman
Take a warm pan, add oil, add onions.
The higher the temperature of the pan, to about medium levels, the more frequently the onions need to be stirred in order to not burn them.
Lower temperatures take longer to produce the caramelization but mostly give a more uniform result, as one can keep the onions on the heat longer.
You'll need to find out what heat works best for you by experimenting a bit.
Also different oils make for different flavors, I prefer x virgin olive oil.
cooking.stackexchange.com/users/7092/Frankie
Often recipes ask for caramelised onions.  What are some good techniques for cooking them this way, as it seems to take a while, and often even if they are on a low heat they can brown a bit too much if they are not stirred continually.
How to caramelise onions?
cooking.stackexchange.com
<onions><caramelization>
cooking.stackexchange.com/questions/2391
cooking.stackexchange.com/users/210/Sam Holder
You need to cook them low and slow with constant stirring, but may want to add a little broth (enough to evaporate) and some salt in addition to the oil. To caramelise onions they need to be cooked slowly over a low heat. Try add a little broth to stop them drying out.
Onions should be cooked slowly on a low heat with constant stirring. You can add some broth to stop them drying out during cooking. You can also add a bit of salt to draw out the moisture.