United Kingdom
I think the United Kingdom itself maybe be emerging to be an early 21st century super power with the US as the world hyper power. Here's the reasons for me thinking this:
Second to the US in world diplomacy
Second highest defence budget
Second largest navy in terms of tonnage
Second most power projection capability
Second largest aircraft carrier fleet with second largest aircraft carries being built after the Nimitz aircraft carriers
UN Security Council seat and founding member
Head of the Commonwealth of Nations (the largest organisation of states after the UN)
The British monarch is also Head of State of 15 other countries such as Canada, Australia, and New Zealand
Major player in NATO and EU
Large North Sea oil and gas production
London being one of the greatest cities in the world 
City of London being the world's main financial centre in terms of number of amount of money that passes through it each year and largest gathering of financial groups.
Pound Sterling one of the world's top currencies alongside US Dollar and Euro
Second highest growth for major developed economies after US.
Its own nuclear missiles on nuclear submarines which have joint longest range with US nuclear submarines
Largest number of over seas territories
Carried out major invasions of Yugoslavia, Afghanistan, and Iraq. 
Was only the nation to actually invade Afghanistan and Iraq alongside US forces (Other forces came after US & UK forces had secured the countries)
Second largest force in Iraq and Afghanistan 
Leads the fight against Afghan rebels in Helmand province
Controls southern Iraq and large areas of Afghanistan
Leads NATO force in Kosovo
The leading nation in tackling global warming
A leading country in the Middle East road map to peace
Most involved in Darfur issue
Second most involved in Iran nuclear issue
Single handedly resolved Sierra Leone issue
I think since the end of the Cold War to present the United Kingdom has played the second largest role in the world after the United States, and after all the role a country plays in the world is what defines a super power. Also the United Kingdom demonstrated that it can single handedly and quickly defeat a regional power and quickly resolve a conflict when it won the Falklands War. This is more than what can be said for such countries as the United States or Former Soviet Union. After the Second World War and during the 1950s the United Kingdom was considered to be a super power because of the role it played in the world but the after effect of the Suez crisis made this disappear. The Falklands war and Thatcher-Reagen era displayed the UK was preparing to retrieve its status as being on the same level as the USA and USSR. Soon after this the Cold War ended and with no Soviet Union left to counter the United Kingdom in any way (like in the Suez crisis) the Thatcher-Reagen duo had worked and the United Kingdom set in motion activities to reclaim such a postion it had in the world that it had in the world before the Suez crisis in time for the beginning of the 21st century. The 1990s was a bit of a prelude to today and saw the United Kingdom slowly begin to prepare as being a power equal to the US and former USSR by being eager to greatly contribute to the Gulf War and and Yugoslav wars and grew more involed in Western Africa by sending troops there to resolve conflict in Sierra Leone and was testing its place as second most powerful in the world to the US and in being a semi super power again. Soon afterwards September 11th happened and the War on Terror that followed gave the United Kingdom just what it needed to reassert itself on the world stage and came just at the right time to have given the United Kingdom time to perpare and try out its future after the end of the Cold War and for the beginning of the 21st century. Today the United Kingdom is easily seen as being second most powerful on the world stage diplomatically and even militarily and could be called a semi super power. People have started to raise this issue called the British Moment in the 21st century. The United Kingdom also acts very much as a deciding force in NATO and the EU in which policy they take or their futures in whether it decides to side with the US or EU and can have an effect around the world. It also greatly influences the other 52 members of the Commonwealth of Nations which it heads by its monarch and is the largest body other than the UN. Not to mention its influence and veto power of being a permanent member of the UN Security Council.