I live in Germany and have an EU passport; my wife is here with me. She is from Macedonia but she has received a five year resident visa. I would like to know if she needs a visa to visit the UK. We are planning to go for four days in March for a football match. We have already purchased plane tickets, made reservations for a hotel, etc.
Bad news: The visa policy of the UK is separate from that of the Schengen countries, so having a German residence permit will not in itself allow your wife to enter the UK.
Good news: However, as an EU citizen your right to free movement within the EU includes a right to travel to the UK with your family, so as long as your wife travels with you, she should have the right to enter the UK without a visa if she has a German residence card headed "Residence card of a family member of a union citizen". (Which she should if you're not German; if you are German she has to apply for a visa, but can't be required to furnish other documentation than for the legitimacy of your marriage).
Bad news: The UK government has refused to implement this part of the Freedom of Movement directive.
Good news: In December 2014 the European Court of Justice ruled that they have to.
Confusing news: It is not clear to me whether this has caused a change of actual practice at the border yet.
What this means to you is that to play it safe, your wife should apply for a vistor visa to the UK. Be sure to note at the time of applying that she is the spouse of an EU citizen traveling with her; I think the UK does honor the part of the rules saying that the visa application fee should be waived in that case.