I normally don't do this, but I know it can be very helpful if you have trouble visualizing what it can look like on a whole wall. Last but not least, find a friend that has an eye for color and ask for help. But do remember that it is only paint and can be changed fairly easy.
By the way if you have picked a color and want to paint this weekend Sherwin Williams is having a sale this weekend. (no, they did not pay me to say this)
And valspar has this on their facebook page too