I do a lot of night paddling in an urban area where other boating traffic is common. In a lot of cases, boats aren't using a light thus you have to really look for them and listen for a boat motor. One way to increase your visibility is to have a waterproof light on you. What you don't want to do is blind yourself with your own light thus reducing your night vision. I put a light on the back of my Type 3 PFD. Friends use headlamps which are great if you're paddling solo, but if you turn to your friend next to you - they'll get blinded, not cool.
The product below sticks on your board or kayak with a suction cup and has two light settings - strobe and a continous light. In many boatin areas, small watercraft such as boards and kayaks are required by the Coast Guard to use a continous, not blinking light. Check yor local regs just in case.
The Hydrostar light is made by Seattle Sports.