I am really enjoying this tool that I found on House Beautiful's web page. I like it because I can pick the exact colors from Benjamen Moore and Sherwin Williams that I am considering and see how they look in a room. Of course, I would never rely solely on this tool to pick a color but it helps get an idea about the color and how it relates to other colors.
When I was building my new house, I spent over $100 on paint samples and painted a small section (about 3' X 3') of each wall the color that I was considering for that room. It was money well spent because that is the only way to really know what the color will look like. Lighting in your specific room will make a big difference on how the color comes across.
Since we are not sheet rocked in yet, and I want to get a head start on my colors, I have been painting poster boards the colors that I am considering. This has been helpful because I can take the poster boards with me to the tile store and make sure that I am picking tile that will go with my color scheme.
Just so you know, Sherwin Williams is the best place to buy paint samples. They will make up a sample for about $5 and it doesn't have to be one of "their" colors. Other places will make up a quart for you and charge full price. Benjamen Moore has some $3.99 samples made up - ready to buy - but they are limited as far as colors.