Where do you live? You mentioned being close to the beach - if you are in SoCal there are some really good bike paths, one of my favorites is the one that goes from Santa Monica to Redondo Beach (if memory serves). I have several bikes but I find I prefer my hybrid/fitness/flat bar road bikes for most rides, unless I am riding in a group on road bikes and need to keep up.
I would say look for a used Giant Rapid or Escape, or Trek FX.
These are great all around high quality bikes, and there is no shortage of used ones for sale - if you live in a populated area (like LA), than Craigslist is a great place to look.