I've arranged to play an organ a few weeks or months from now, and would like to know, what pieces are there which are very powerful and awe inspiring in the sense that you get lost in the music when listening to them, especially pieces which use very low pedal notes. Preferably baroque, and not too hard on the pedals as I am a complete beginner to organs.
Thanks,
Carl

Forgot to mention I would like minor pieces.
Thanks,
Carl

Definitely this one:

http://en.wikipedia.org/wiki/Symphony_for_Organ_No._5_(Widor)

The Widor Organ Symphonie (as previously suggested) is really impressive particularly the Tocata Movement, as well as Bach's Tocatta and Fugue in G Minor would meet your stated requirements, but I think as a beginner both of these pieces would discourage a beginning organist. I would suggest possibly starting with a good organ method like the One written by the late Harold Gleason, former head of the organ department at the Eastman School of Music. The Gleason Method will give you some repertoir to work on as well as provide instruction in organ technique. Flor Peter's also has a collection of organ pieces I believe it's called "The Little Organ Book" that has some progressive literature that you can work through. The organ both the Manual's and the pedal board require diferrent technique than the piano, so don't expect to jump into literature that is at the same level as what you play on piano. You'll need a good organ method book that explains the differences, and a competant organ teacher would be a big help also.

I really intended humor. The Widor is one of my favorite pieces but it takes a skilled organist to pull it off.

I wonder, though. If his organ has MIDI input, it might be possible to let the computer handle the notes while he does the registration, to get the feel of what those impressive pieces sound like from behind the console. Just a wacko thought.

I'm not familiar with a g minor toccata and fugue by Bach. I'm familiar with 2 in d minor and the f major. What's the BWV#? The rest of your post is absolutely right, but I don't know if the Gleason method is still available.

To answer the original query, the organ is not an instrument you'll be able to just pick up. First of all you'll need the right equipment (shoes) to play the pedals. For that I would consult an organist. Many playing techniques are different, unless you're playing a tracker instrument a light touch is all that's needed and be prepared to do more finger substitution that you thought possible. There is no sustain pedal so you have to actually hold every note for its proper rhythmic value.

My suggestion would be to play some Bach WTC on the organ because they usually translate pretty well to the instrument. Play a c major or minor and you can add the bottom note of the pedals at the end to satisfy your desire for deep bass.