Crysis is a great example of non-repetitive sound design, this is true for the ambience/ sound effects as well as the music.
For a start there were 3500 sound events used, nearly 15000 individual sound files, all in all taking up 1.7GB on the DVD disc!
To create a non repetitive ambience the sound designers have done much more than randomise timing, pitch and velocity of sounds. They have marked across the map for sounds, overlapping areas and placing them inside each other as well as prioritising sounds based upon the location of the player. To add realism on top of fighting repetition the ambience has been given dynamic behaviour, for example a bird sound ends when gunshots are fired. Pretty sweet!
The music is very cinematic and succeeds in being non-repetitive. The sound designers apparently used a system of nodes. I assume this links in with the varying levels of intensity in the score to produce arrangements of music that will be slightly different every time you are in action of a defined intensity.
Also worth noting is that even though the music was designed to crossfade seamlessly, they still covered the transitions with sound effects wherever possible so not to jar the player. I find this to be a really cool idea, I think it's an inventive way of dealing with transitions.
The Gamasutra post about the Crysis audio team speaking at the GDC this year is definitely worth a look http://www.gamasutra.com/php-bin/news_index.php?story=17530