One of the most famous landmarks of Britain, the London Eye, a 135m ferris wheel, opened back in 2000, shortly after the millennium. As well as being the biggest of its kind in Europe (was the biggest ferris wheel in the world until 2008), it is also the biggest tourist attraction in the UK.
Standard tickets are about £17 (€21) and offer some of the best views of London. Samsung Galaxy tablets,installed in the pods, offer details and a brief history of the visible landmarks, including Buckingham Palace, the houses of parliament and Westminster Abbey.
It is worth noting, you may have to queue for a while, but it is worth it in the end and there are also fast track tickets available if you are willing to spend a bit more money. You can also buy tickets which include admission to the London Eye, Madam Tussaud's, the London Dungeons and the Sea Life Centre, which is cheaper than buying them all individually.