West Marine
Cetol Marine makes Sikkens, you can get it at West Marine. I use the Satin, it looks good and lasts. Be sure to sand if your teak is rough. A good two part cleaner like Semco couldn't hurt proir to sanding. Just like painting, surface prep will yield good results. Three coats are required for the first application, then it's one coat per season after that. If you did a good job, it sould look good for 5 - 8 years before it starts to flake or discolor. At that point it's very easy to sand off and re-apply.