I hate castrandom. It seems sloppy, and it never perforoms well for me in my tests. I usually go up against some training dummies, or a boss fight and test out new spam macros. Here is what I am using with my shammies now, I have two different spawm buttons, one for trash, one for bosses, and I have earth shock and chain lightning on keys explicitly for them.

Trash Spam:
#showtooltip Lightning Bolt
/use 13
/use 14
/cast Elemental Mastery
/cast [target=focustarget][target=focustargettarget][harm] Lightning Bolt

Boss Spam:
#showtooltip Lava Burst
/use 13
/use 14
/cast Elemental Mastery
/castsequence [target=focustarget,harm][target=focustargettarget,harm][harm] Flame Shock, Lava Burst, Lightning Bolt, Lightning Bolt, Lightning Bolt, Lava Burst, Lightning Bolt, Lightning Bolt, Lightning Bolt

These are pretty similar to many of the other macros people have posted, and I think it is as near optimal as possbile, Just be sure to adjust the number of LB's between your LvB's to reflect your haste.