The best (ok, only) Cedar Plank Salmon I've ever had!

2 Tbsp. fresh squeezed lemon juice.. or 2 Tbsp out of a bottle...
1/2 cup pure maple syrup. NO SKIMPING ON THIS ONE!!!
1/3 cup soy sauce
1/4 cup water
2 crushed garlic cloves.. or a reasonable equivalent of the crap in a jar...
1 tsp finely chopped ginger. You wouldn't believe how finely chopped ours was! Some would swear is was powdered junk...
Mix everything in a saucepan and heat over medium heat until it just starts to bubble then set aside to cool.
This is enough marinade for four nice centre cut fillets... about 2 lb worth (just under a kilo)
Marinade the fillets in the cooled sauce for at least an hour.
Place the fillets on the cedar plank that has been WELL soaked (> 4 hours). Skin down!
Chuck the plank on your bbq and cook till done. Varies like crazy based on your bbq. but...
Ours took about 20 minutes to come up to just under 130 degrees old school (that's Fahrenheit)
Baste once with the marinade.