IMDB has related movies/suggestions as well as Amazon (read the comments also, there might be more mentioned.)... sometimes you find other gems along the same line you were thinking.
Look at the production company, director, author and see whatever else they are attributed to.
One place I can recommend to finding a good movie blind is looking through the "Criterion Collection" videos and DVDs (Hulu has many of em, but not all), which is like the ultra-fan special edition of classic films, most of those are notable for some reason or other.
Lastly there have been several threads here on great books movies, do some searching and you will find em.
For music (besides amazon) - if you like particular genres check out some streaming radio stations - i.e. for the jazz fan Play Misty For Me radio or Luxuria... There's a streaming station for just about any interest. Shoutcast is a good place to start hunting for streaming stations.
"I'm going to watch a movie tonight, what's a really good movie that I probably haven't seen."
This works best with strangers or people you've just met. I find that people who know me always recommend movies that I've either already seen, or decided that I don't want to see. If the stranger has any affinity towards movies, they can almost certainly come up with a gem that you've never heard of.
I discovered this works when I asked this exact question of someone on a whim and they recommended "Castaway on the Moon". It was a darn good movie, that I never would have found/watched on my own. I've since asked this question of all sorts of people with great results.