My own beach time favourites (when the kids leave me long enough to read, that is!):
High Fidelity - Nick Hornby. Hilarious insight into the life and thoughts of a typical city male in his thirties. Actually, anything Nick Hornby will do. "About a boy" is also very good.
All the Lord Peter Wimseys by Dorothy Sayers. Although written more than 50 years ago now, they don't seem the slightest bit oldfashioned. Keen sense of humour, keen understanding of human nature.
Dune - Frank Herbert. Classic SF. If you don't like Science Fiction or anything like it, don't bother with this one. Otherwise it is complex and exciting, and it is really about humanity and moral conflicts rather than technology. Good SF almost is, I find.
Tigana, A song for Arbonne, The Fionavar Trilogy - Guy Gavriel Kay. Best fantasy writer since Tolkien. A lot of authors can make me excited, caught up in the action or make me smile. Guy Gavriel Kay can do all of that - and make me cry too. A song for Arbonne is the least "fantastic" of them, with very few of the usual fantasy elements - enchantment, fictional beasts, wizards etc. - included. The Fionavar Trilogy is basically a modern Lord of the Rings. Tigana is something in between. All of them are marvellous and very romantic in the original sense of the word.
A hitchikers guide to the Galaxy - Douglas Adams. Pure nonsense, pure delight, plenty of laughs. Don't read it if the plot matters to you.
Almost all of the novels by John Le Carr?. His spy novels are a very far cry from all the James Bond glamour, quite often with a sadness and melancholy about them. The Russia House is a spy novel as well as a beautiful love story.
Fanny - Erica Jong. Written as if it is the true memoires of an 18th Century young girl and her life as a prostitute, pirate, author, mother etc. Brillant.
And then - if you really want to switch off your brain and basically just relax: Most of the novels by Victoria Holt. It is like Barbara Cartland, only better written and with more compelling characters. If you read one, you will know how all of them end and guess all the improbable twists along the way - but still delightful enough if you don't want to think at all.
Enjoy,
Regards, Susanne