More about the sites you might visit:

Westminster Abbey
Famous as the resting place of Britain's monarchs and cultural icons and as the site of its royal coronations and weddings, this elegant medieval church is one of London's most important and beloved buildings. (Allow 1 hour)
Admission: Adults £27; Children (11-16) £12
Open for worship only, no tourist visits, on Sundays.

The Tower of London
Officially named Her Majesty's Royal Palace and Fortress, The Tower of London was initially built by William the Conqueror in the 11th century. The complex is the repository of the Crown Jewels and the historical site of the demise of many opponents of former English kings, among other things. (Allow 120 minutes)
Admission: Adults £26; Children (5-16) £12

Buckingham Palace
Buckingham Palace has been the royal London residence and offices of the monarch since the time of Queen Victoria. It is also used for state occasions such as banquets for visiting foreign heads of state. The State Rooms are open to the public in the summer months. (Allow 120 minutes)
Admission to the State Rooms: Adults £31; Children (under 17) £17

Churchill War Rooms
This is the secret underground headquarters that served as the nerve center of Britain's World War II effort. Shortly after becoming Prime Minister in May 1940, Winston Churchill visited the 'Cabinet War Rooms' to see for himself what preparations had been made to allow him and his War Cabinet to continue working throughout the expected air raids on London. It was there, in the underground Cabinet Room, he announced, "This is the room from which I will direct the war."

Also within the Churchill War Rooms, is the interactive Churchill Museum, dedicated to the life and achievements of Sir Winston Churchill. (Allow 90 minutes)
Admission: Adults £26; Children (under 16) £14

The British Museum
This rich collection of 7 million objects includes some of the most celebrated artifacts of ancient Asia, Egypt, Greece, and Rome, housed in the world's oldest public museum. The museum's holdings span two million years of history and culture. (Allow 90 minutes)
Admission is free to all visitors.

The Tate Modern
This is Britain's national gallery of international modern art, dating from 1900 until today. The most-visited modern art gallery in the world, it is host to some 4.7 million visitors per year. (Allow 1 hour)
Admission is free, except for special exhibitions.

The London Eye
The London Eye is a giant 135-metre (443-foot) tall Ferris wheel situated on the south bank of London's River Thames. It is the tallest observation wheel in Europe and the most popular paid tourist attraction in the United Kingdom, visited by over 3.5 million people annually. On a clear day, it is possible to see as far as Windsor Castle! (Allow 1 hour)
Ticket prices: Adults £49 & children 4 & up £42

The Globe Theater
A modern reconstruction of the original theater most closely associated with William Shakespeare, "Shakespeare's Globe" was opened in 1997, approximately 750 feet from the site of the original. (Allow 1 hour)
Admission: Adults £12.50; Children (5-15) £8.00
Closed December 24 & 25

The Shard
Admission: Adults £38; Children (5-15) £33
London's highest and unparalleled 360 degree view of the city!

HMS Belfast
Admission: Adults £20; Children (5-15) £10.
HMS Belfast is a Town-class light cruiser that was built for the Royal Navy. She is now permanently moored as a museum ship on the River Thames in London and is operated by the Imperial War Museum.

London Dungeons
Admission: Adults £38; Children (5-15) £31
One of London's most iconic and unique attractions. The London Dungeons recreates various gory and macabre historical events in a gallows humor style using a mixture of live actors, special effects and rides.

Madame Tussauds
Admission: Adults £60; Children (5-15) £60
Lifelike wax figures of the world's most famous!

Sea Life Aquarium
Admission: Adults £37; Children (5-15) £31.
Find out about penguins, sea turtles, sharks, jellyfish and much more!