Katie just sent me a good one from Mad Men season 3:

There's no use crying over fish in the sea.

Much delayed update!

Well here's a few more. Hey - it's better than nothing!
From Chloë:

I overheard someone say "It all boils down to the wire"
Grasping at the last straw

From Gio:

Shoot fish in a barrel fist, ask questions later.

A few cracking mixed metaphors from me
You can't walk on eggshells without cracking a few eggs.
You can't put all your eggs in one basket without cracking a few eggs.
Don't count your chickens before you've cracked a few eggs.

And Louis pointed me towards a scene from the movie Boondock Saints, which contains the following:

People in glass houses sink ships.
Don't cross the road if you can't get out of the kitchen.