Bournemouth Beach is one of the best beaches in England - it is several miles of golden sand, the waves can also reach a decent height (for England) and is therefore popular with surfers. The beach can get crowded in the height of Summer so I would recommend getting there early to get a good spot!
Bournemouth Beach
Sandbanks is a coastal region located between Poole and Bournemouth. It is currently the 4th most expensive area in the world to buy land on - many of the houses are well in excess of £5 million. The main housing street in the peninsula is aptly named "milionnaires row" due to the sky-high prices in the region. Recently a bungalow that was pretty much in a derelict state went on sale for £4 million, indicating the demand for land in Sandbanks. Sandbanks Beach is another highly popular beach, about 3 miles long and boasting extremely high quality for an English beach. There are also a range of activities on the beach such as canoeing. A crazy golf course is another popular destination - a good bit of fun for the whole family.
Sandbanks
Poole is a good place to go as well when the weather is nice - it offers a wealth of boat trips, as well as many restaurants with good food. Brownsea Island, just opposite Poole Quay, is a little National Trust Island and is worth a look around, you can walk round the whole island in a couple of hours. It is also one of the few places left in the UK where red squirrels still live in the wild.
The Dorset coastline is one of the best holiday destinations in the UK, due to its fine beaches and range of other activities aside from the obvious sunbathing. It is definitely worth a visit.