It might not be needed for you to get a Visa after all. You have not given enough information to answer that question to the fullest. But I'll post a list of countries that DO need a Visa if their stay is under 90 days.
For David,
You're right that the United Kingdom isnt subject to the laws governing immigration concerning the Schengen area. I just do not see how you can boldly state someone needs a Visa if you don't know what country's passport the person is holding.
I am from South Africa and am planning to stay with a friend in Holland over the period 17June to 07 July 2012. Do I need a Schengen Visa to travel to the UK, if yes can I get it that side and at what cost. We are planning to stay about 1 day on that side.
The UK is not part of the Schengen Zone, so if you want to travel to the UK you'll need a UK visa, as well as a Schengen visa for Holland. You can apply for one at your nearest British Consulate in South Africa.