I like to eject my external drives because they slow down my mac when they spin up, but I want to have an easy way to access them if I need to. I wrote a little AppleScript that will toggle the mount status of the drive (if it's mounted, it will eject, if it's unmounted, it will mount).
To run the script, use the script menu at the right of the menu bar, or bind it to a hot key using a Quicksilver-type app. Be sure to change 'YourDiskNameHere' to the name of the volume you're working with.
The script can be easily adapted to only eject, or only mount the drive. You can also tweak it to display a Mount/Unmount dialog if you wish.
set diskName to "YourDiskNameHere"
tell application "Finder"
if disk diskName exists then
eject disk diskName
else
tell current application
set deviceLine to (do shell script "diskutil list | grep \"" & diskName & "\" | awk '{ print $NF }' }'")
if deviceLine = "" then
display dialog "The disk \"" & diskName & "\" cannot be found." buttons {"OK"} default button 1 with title "Error" with icon caution
end if
set foundDisks to paragraphs of deviceLine
repeat with i from 1 to number of items in foundDisks
set this_item to item i of foundDisks
if this_item contains "disk" then
do shell script "diskutil mountDisk /dev/" & this_item
end if
end repeat
end tell
end if
end tell
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120211184732735