One of the best mods for Morrowind was the "atmospheric sound effects" mod. Is there anything similar for Oblivion? I'd really like some immersive sounds when the music isn't playing. Thanks in advance!

Not familiar with that particular Morrowind mod, so I might be way off here, but...

http://tesnexus.com/downloads/file.php?id=5861, http://tesnexus.com/downloads/file.php?id=14344, http://tesnexus.com/downloads/file.php?id=19038, http://tesnexus.com/downloads/file.php?id=29676, http://tesnexus.com/downloads/file.php?id=24622, http://tesnexus.com/downloads/file.php?id=24602, and http://tesnexus.com/downloads/file.php?id=7703 ... might appeal. :shrug:

Actually, not so much "and" in all cases. There would be some amount of "or" too.

http://www.tesnexus.com/downloads/file.php?id=18305 also allows you to hear weather indoors as well as improving atmosphere in other ways

Indeed. Good call.

Along vaguely similar lines, you might also like http://www.tesnexus.com/downloads/file.php?id=13987 and/or http://tesnexus.com/downloads/file.php?id=26892.

Tangential, both, but nonetheless great.