If you want to go farther west to Santa Monica, there's a place called Blazing Saddles on the Santa Monica Pier that rents what looks to be decent equipment. The pier is on the beach bike path, which runs about 18 miles south and 3 miles north. Minimal hills, cool breezes. Just keep in mind that if you go south first, you will most likely have a headwind component coming back north. For a longer ride you can go inland along Ballona Creek for about 5 miles from Marina del Rey.