There aren't any beach bags, per se, but I want to mention a company Melly & Me, out of Australia (sisters Melanie and Rosalie have several commercial bag patterns available. I already mentioned Rosalie's patterns in an earlier post).
They also have an etsy shop.
Here's a bag one of their blog readers, Cathy of Miss Marzie, made from their 'Sunshine' pattern out of tea towels--isn't it incredible?
Another reader, Lisa of Pink Lemonade Boutique. made this gorgeous scrappy log cabin bag using the tutorial on the Melly & Me site.
Their newest pattern is called 'Sherbet'