Now that I am using XMonad I find that my USB devices no longer automount when I plug them into my computer. How do I get them to automount again just like they did when I was using gnome?
I'd recommend one of the udisks-based solutions. uam seems to do the job without too much configuration. udisks-glue is also decent for scripting.
This is just simple tool for mounting pendrives and alikes when inserted -- something like ivman or functionality integrated in KDE/GNOME.
udiskie is a simple daemon that uses udisks to automatically mount removable storage devices.
The way that I have solved that problem is to use nautilus running the the background to continue to manage that for me. You can do that like so:
nautilus --no-desktop -n &
If you happen to start XMonad using a custom .xsession file then that would be the perfect place to put that line. Make sure you put it before the 'exec xmonad' command.
I think you are better off with udisks. It comes installed by default (at least on Ubuntu) and handles the standard mounting and unmounting like a charm. You can read all about it here - https://help.ubuntu.com/community/AutomaticallyMountPartitions
Btw as the documentation says, udisks is not gnome specific.