Negrini's right about small amounts of power. My solar panels (measuring approx 25" x 50") deliver ~2 amps at ~19V (they're 15 years old).
If you're going to get a regulator, get one specifically designed for solar applications. They run between $40 and $80 depending on the amperage they have to regulate.
I said, "if" because you may not need one as I explain below.
When I first got the boat there was no regulator -- panels were directly wired to the largest battery bank (~400 amp hours in size). The PO had lived aboard the boat continously for five years and said he didn't think a regualtor was necessary. After I bought the boat we kept it at a dock, and I decided to avoid shore power and to use the panels to keep the batteries charged. One weekend the first year we owned BR, I arrived at the boat to find the batteries at 15 V. Obviously we'd had a very sunny week and, with no load on the battery banks, the panels had overchardge the batteries in spite of the fact that I had connected both large banks (totaling 800 ah) together. I bought a regualtor and used it until it failed (for reasons unkown). At the time it failed were living aboard in the Caribbean I decided not replace it. My rationale was that if you're using the batteries everyday and if you keep at least some load on them 24/7 you don't need a regulator because you're not going to overcharge them. Now that we are not living aboard, I have installed a new regulator. Last summer the panels kept the batteries charged to the proper voltage and the frig cold while we were away from the boat.
PS - I see that while I was writing this post Cam has done one with much more specific info on regulators. I now use a 7amp $40 regulator, but if I ever get around to replacing my panels with newer technology and higher W output, I will consider one of the new high tech chargers that claim to boost your amps to the battery by 25% or so. Neither of these events will occur, however, until the DJIA reaches 12,000.