What exactly is a "real" revolution is often debatable. Let's assume for the sake of argument that it is a change in government that most people would consider to be a significant departure from the previous government.
When you hear of revolutions from books or other people, it often involves some kind of bloodshed or violence - perhaps even some sort of civil war.
What follows are some types of revolutions that do not involve the shedding of blood.
These revolutions happen within the existing constitutional framework of the country.
This type of revolution usually does not happen quickly, but perhaps slowly over a short number of years. It happens when nearly everyone within the society decides to change their behavior, perhaps because of new scientific discoveries or compelling new ideas in social organization. It may not even involve a change in the actual people in government - instead, the people just start doing things differently.
Voting for Revolution
This type of revolution occurs only at the ballot box. Voters may decide to vote for politicians entirely different from the ones they voted for in the past, or the legislation passed may be entirely different from past legislation.
While the revolution imagined in popular culture may involve an armed militia overthrowing the existing constitution, the constitutional process itself can still be used to completely change it. For example, if some nation's constitution requires 70% of the vote for approval of changes, then 70% of the people could vote in so many changes to the country's constitution that it is virtually unrelated to the constitution before the "revolution".
Civil Disobedient Revolution
These revolutions involve peaceful, but flagrant violations of existing legal norms.
Mass Civil Disobedience
This involves changing the government by organizing very large numbers of people to openly defy the law. If even large sections of the police population join in, then the political system would have effectively changed, even without actual legislation.
A variation of mass civil disobedience that focuses on not going to work. Strikers hope to force the minority of government and business officials to respect their demands or else they would bring the country to a standstill. If there is enough support for the strike, then the officials themselves may be replaced.
Occupations and Takeovers
These movements often have the potential to result in some violence, even if violence is not the actual intent. In order for an occupation or takeover to work, the occupiers need to be able to make use of whatever it is they are occupying - which means this is usually the employees of a company or organization that are involved.
In these occupations, employees assume democratic control over their places of work. If they are unmolested, then they carry on doing the work of the companies or organizations. However, because the companies are now controlled by different people, significant change may sweep the country. If they are attacked, either by police or hired thugs, those engaged in non-violence would either run, allow themselves to be arrested, or allow themselves to be beaten.
Takeovers with Self-Defence
This is similar to the non-violent scenario above, except that the revolutionaries are willing to use self-defence. As long as they are unmolested, they are virtually indistinguishable from the non-violent (except, perhaps, for the presence of weapons on the premises) - they merely carry on changing the behavior of the organizations they now control. However, when attacked, the "revolution" would no longer be bloodless. Thus it falls in the hands of the attackers to determine whether the revolution would be bloodless or not.
StrawberryFrog says examples of bloodless revolution ? South Africa, 1994 had a negotiated consitutional change followed by a vote, Czechoslovakia had mass demonstrations in the 1989 Velvet revolution...