How can I know which DVDs will play on my system?

There are plenty of questions where people essentially want to know how to play their DVDs (How can I play encrypted DVD movies?, Lord of the Rings, Toy Story, another one).

Is there any way to know before you buy a DVD to know if it runs on your system?

Obviously, simply looking at the DVD does not help:

Is there any online service or another way to get to know if you can watch a DVD on your computer before buying it?

edit: Sometimes, Amazon customers give this information if it is not working. But I would also appreciate a "white list" of DVDs that do work.

As long as the region code on the DVD disk is compatible with your DVD player, it is fine. Instead of knowing a whitelist of DVD disks, it will be better if you know the compatibility of your DVD player/drive.

http://www.doom9.org/index.html?/rpc1.htm the above link provides some info on how to check (and how to modify)

An alternative solution is to upgrade your player to bluray. All bluray discs are region-free, and you will not worry about incompatibility issues.