Sharks with frickin’ laser beams attached to their heads
The LEGO Agents Speedboat Rescue (8633) set has a set with laser sharks. The set uses a new version of the LEGO shark with two studs on the top behind the head. 



Sadly the shark only appeared in two sets, this one and Brickbeard's Bounty (6243) and because of their limited release they are very expensive on Bricklink.

For the original shark you could use a small Technic rubber band (or any small rubber band) to attach a laser. 

In the example below, The body of each laser uses a Technic pin joiner, the rubber band runs along the slot in the brick so it's kept in place. The back end of the laser is joined together with a flexible rubber axle connector.