I specialize in properties for sale in L.A.'s beach cities and there are all kinds of townhomes, lofts, and condos in and around the Marina (and in Venice.) There's been a glut of units on the market over the last few years, especially in the larger, newer loft complexes, the premier Marina Pointe Towers, and in Playa Vista. A lot of interesting units in smaller properties are also usually available.
In my opinion, the best values around Marina del Rey in terms of potential appreciation and lifestyle are the single-family homes just east of Lincoln Blvd./PCH south of Washington Blvd.. These modest mid-century houses which are on full sized lots routinely sell for only $600 to $700k and they're just 2 or 3 miles from the beach. Along with similarly priced homes in Venice, these may be some of the best real estae values in the city when you consider the finite supply of land by the beach and the growing trend towards high-density development in prime areas.
I'll be glad to answer any questions that you have about these and other properties available around the Marina, Venice, or Playa del Rey and you'll find all of the listings currently available on my website.
Best of Luck.