I know there is a lot of praise about different tower speaker set ups and brands, but I just wanted to give a shout out to Liquid Acoustics. I installed a pair of the Liquid Acoustics double tower speakers at the beginning of 2011 boating season powered by a Fosgate T600-2 amplifier. And I was pleasantly surprised once I cranked them up, but even more so on the water. They have exceptional sound at all volumes, warm tones and musical. I put 120 hrs on our boat last year, mostly towing, and probably twice that sitting and listening to music. Every time I crank the speakers up I am amazed at the clearity and the ability to hear the speakers at any tow length. Be it at the end of the 80' wakeboard rope when cutting completley out or 20' behind the boat surfing they still have great musical tones. Although the speakers are extremly loud and clear behind the boat the volume in the boat is very minimal, to the point were you are able to hear instructions from the passengers without yelling.
I know there is a lot of boaters looking for a tower speaker that sounds great and won't break the bank. If this is the case I can vouch for the Liquid Acoustics Dual LAXP-D8 wakeboard tower speakers. They are a little heavy, which were some of the concerns I had, but the tower has no problems handling the weight even in rough waters. They also are very easily installed and removed from the tower for transport (less than 2 minutes per speaker)
I am not affiliated with them in anyway just an extremely happy customer that has put there product to the test and wanted to pass the word on. (Even though there is a pic on their web site of my install) You can also see some pics of my install in my stereo install albums if insterested.
You can find them on ebay directly from LA for a steal right now.
Just my thoughts and opinions and by no means a stereo expert.