If you're under the age of 31, you can apply for a Tier 5 visa, which used to be the Youth Mobility Scheme. Basically there are a few criteria you need to meet, and the possibility of being accepted is quite high.
If you're over 31, you will have to get the Tier 1 or Tier 2 visa. The first one is for professionals, and the qualification is quite high, but if you're degree-level educated with significant experience, you may be in luck. Other than that, the Tier 2 is one that's applied for by a potential employer from the UK. It's the hardest one to achieve, from what I can see, as in order for a
UK employer to apply for this, they have to prove that they cannot fill the position with a UK citizen/resident, or a member of the EU. That process makes it both long and hard for foreign applicants.
The border agency website has lots of good information on this, so I'd check it out if you get the chance.
Good Luck!