Brazil is a year round destination [except for the southern part of the country]. Beware of Brazil's summer holiday Dec-Feb [school holidays and Carnival time], when domestic transportation and accommodation can be expensive and difficult to find.
In summer, Dec-Feb, temperatures can reach 40C. Best March-May and Sept-Nov.
Generally sand is white and fine, the sun shines, prices are low and people are pleasant. The water, however, is the Atlantic Ocean, so will often be rough, with strong currents, a steep drop off and not very warm, unless protected by a reef. Careless tourists drown regularly!
Around Rio de Janeiro:
Copacabana, Rio de Janeiro
The world's best city beach with 4km of surprisingly spotless wide white sand. Relatively cheap, with friendly, lively locals. Plenty of accommodation, restaurants and outrageous night clubs. A great place for volley ball, and is the home of 'futevolei' [foot volley ball], too. Fun for people watching especially if you favour huge bottoms.
The down side is that you have to be cautious about thieves : use common sense - no watches, jewellery, or cameras.
If you like a little more sophistication go next door to Ipanema.
Ipanema and Leblon, Rio de Janeiro
Home of the bikini and tangas- tiny bikinis- Ipanema and Leblon are adjacent and slightly more chic and relaxed than nearby Copacabana. There is a family-friendly ambience and even a meeting area for mothers and babies. Soft white sand and cool blue water.
Angra dos Reis, Costa Verde [between Rio and Sao Paulo]
If you want to escape from Rio, Costa Verde is a good destination. Costa Verde [Green Coast], is one of the most scenic stretches along the 175-mile coastline between Rio and Sao Paulo, where tropical forest spread down to the ocean, with broad bays, golden sandy beaches and small fishing villages. There are some good resort hotels, villas, trendy restaurants and clubs. Angra dos Reis [Kings' Cove] is the best beach of the area and one of the most untouched beauty spots in the country.
Santos Beach Gardens, south of Sao Paulo
The town of Santos, 45 miles from Sao Paulo, has a beautiful 4 mile beach garden, reckoned by locals to be the largest garden in the world. It stretchs from Ponta da Praia, ferryport from another well-known beach resort called Guaruja, to Sao Vicente, the oldest town in Brazil.
Far north of Rio de Janeiro, north east Brazil:
Salvador, Bahia State
A beautiful, vibrant colonial city with excellent beaches on both sides.
Ilha de Tinharé, Bahia state
The seashore on this little island off the coast of Salvador is one of the prettiest in Brazil.
Neighbouring beaches, Ondina and Rio Vermelho, host Salvador's most expensive resort hotels, while Rio Vermelho has some of the city's best bars and music.
Going north along the Orla Marítima are many restaurants, clean white sand, and in the north, the Lagoa de Abaeté, a black freshwater lagoon.
Praia do Forte resort, Bahia State
Praia do Forte, to the north of Salvador, is an old fishing village reconfigered as a laidback, downmarket resort. It has more than 8 miles of superb sandy beaches and natural pools and is surrounded by thousands of square miles of wild nature. Among the many cheap and cheerful little hotels is Brazil's first eco-resort, Praia do Forte EcoResort - delux but low key - lurking by the best sandy bit in the area, and offering various eco tourist programmes such as bird-watching, and rainforest walking. 1.5 hours from Salvador.
Natal, Rio Grande Norte State
Natal, inelegant, but 'the city of the sun' sees more than 300 days of sunshine a year and has some of the best stretches of sand in South America, including good lively city beaches - but beware the surf.
Just out of town the seaside get better with the prettiest area being Ponta Negra bay[ 10km away], and Pipa beach [80km away] - so lovely that dolphins visit regularly to admire it.
In addition Rio Grande do Norte has a more than 40 other great beaches, in particular Pirangi, Jacuma, Maracajaú, Galinhos. And by the way, wild buggy rides over the huge dunes seem to be a big attraction in this area.
Fortaleza, Ceara State
A mediocre city beach but hundreds of miles of superb wild coast either side of it, with dunes, palms, wild water and not much else.
Jericoacoara, Ceará State [300km west of Fortaleza]
Jericoacoara, increasingly fashionable in Brazil, has spectacular sunsets from the sand-dunes overlooking the little developed beaches. It is also known as an excellent place for windsurfing and horse-riding along the sands.
Praia do Rosa, 90km south of Florianopolis
A small fishing village popular with no more than a few surfers until recently, Rosa is a beautiful beach with great surf, but developing rapidly. Get there before it's too late.
Guardo do Embau, near Florianopolis
Between Florianopolis and Garopaba this is a beautiful beach with an excellent slope for sandboarding, a small beach, good surf and friendly locals.
And other suggestions south of Rio: Praia Ferrugem, Mariscal, 4 Ilhas.