Probably the most immediately appealing, and lastingly enjoyable, organ music (to my taste) are the Opus 7 Concertos by Handel - especially in this version played by Peter Hurford:
Then, if you want to try the organ as a solo instrument, I would suggest starting with the Bach Trio Sonatas - which have been wonderfully recorded by Ton Koopman.
In a sense these are untypical of the mass of organ music - both in the type of instrument used (a lighter, flutier sound than usual); and in the genre of music being played (baroque, rather than romantic).
An earlier, more austere and indeed tragic, piece is the D-minor Passacaglia by Buxtehude - which I would rank as a truly great piece of music. Note: A passacaglia is an archaic form of variations in triple time; built over a repeating sequence of bass notes (played on the organ pedals).