obviously depends what your after. Isle of Wight is good but Ventnor and Sandown get v.busy - Bembridge is nice, very chilled, dog friendly beaches and everything you need. Lots to explore on the island and of course in Portsmouth from where you can get the ferry over.
Obviously the SW is good but will be crowded (
http://www.masonsarms.co.uk/) is another favourite of mine if you want good beer, food, quiet beach and not much else.
Other suggestions would be Wales, Pembrokeshire coast is great and Wales always seems so less crowded than England.
Hire a narrowboat and do the Norfolk Broads?
A driving holiday in the Irish republic?
Another interesting option is of course the channel islands of Jersey and Guernsey!
I haven't had cause to go up North or to Scotland much but no doubt there are some fab places up there that other posters can reccomend.