The Navisafe
360 degree LED ($70) is probably the top of the line when it comes to navigation lights, just a bit pricey for just a light. The Yak Attack
Visicarbon Pro ($85) &
VISIPole II ($55) are nice, complete options. They are probably the most popular lights on the market, too. The Tek-Tite
Mark III - 2 LED ($28) is the same light used on the Yak Attack lights and is what I have for my kayaks. (They also have a
4 LED version ($34)) These lights will easily slide into a piece of PVC which can then be slid into a rod holder or mounted to a crate.
As Tallgrass05 mentioned, there are tons of DIY videos and instructions online as well.