I like Valencia's beach, but the city is not much smaller than Barcelona. It is way more laid back, though, and has always been Spain's party capital. It is also sigificantly cheaper than Barcelona. Alicante itself is not a very attractive city, but Malaga is a nice little town. I've never been to the beach, though.
Edit: An alternative might be Gandia, a small town an hour from Valencia by train. It has a very nice beach, and cleaner water than Valencia. Most visitors are Spanish, with foreigners stopping there.