what are you looking to spend in the medium price range? an amazing bang for your buck tower speaker is the kmt6 by kicker. if you want to spend less look for a coaxial style marine speaker in a tub like these http://www.buywake.com/catalog/boat/towerSpeakers/Dbot5
depending on the speakers you pick you will either get a 2 ch or 4 ch amp. some good brands are jl audio, alpine, kicker, polk all make great marine amps and your dealer might have some old in stock he wants to get rid of or you can find another way to get them on the cheap if you want. you won't get a warranty though support your local vendor if he is worth supporting . . i would personally suggest dual batteries and an isolator so you can switch to one battery while relaxing and always have a cranking battery ready to go.