Anyone know of a mod that makes summoned items/creatures have lojnger duration? Or one that allows for more than one creature to be summoned at once? I haven't been able to find a COnjuration mod that does these.

Here You go: http://www.tesnexus.com/downloads/file.php?id=5542

Supreme Magicka has several configurable options for summons, including sustained/permanent ones.

LAME also allows multiple summons...