I'm not very good at matching colours. I can tell when something clashes badly, but couldn't pick two matching colours to save my life.
When creating the template for this site I used ColorMatch 5K to give me 5 matching colours to go with the basic shade.
defencemechanism.com | Color Toy does exactly the same but uses a flash driven page.
Addition: This Color scheme site has loads more options for picking colours and gives more colours in the options.