I think you can team up any colour you like with a brown sofa. (after all the ground is brown and all sorts of coloured plants grow there) Something bright would look great and so would something soft like cream.
Throw out that sofa. Brown is boring. It goes with nothing. Add a little colour to your life.
My leather couch is a reddish-brown. I love different shades of teal, sage, and cream. I bought different pillows for my couch with these shades and I loved it! I bought curtains and small knick knacks to help tie the look in. I think that brown is a versatile color... pick colors you like and go from there. If you get them home and don't like them you can always bring them back!
black, beige, and other shades of brown. White if you like white. Dark orange if you like it. Reds and purples/fall colors.
Almost any color will go well with a brown couch except for Blues and Purples. You can either blend in with creams, tans, lighter browns, or darker browns, or you can contrast with reds, yellows, or greens, depending on the other colors in your room. If you have a lot of "Earth Tones" in the room, try contrasting colors on the pillows and throws. If your room has a lot of bright colors, blend in pillows and throws instead of using the contrasting colors.
You want the total effect to be warm and welcoming, while a little interesting. You do not want the room to be something you walk into and go "Oh wow, my eyes hurt."
Brown is an earth colour so add a variety of "Fall" / Autumn colours
orange, yellow, beige, red, burgandy
well mine is brown leather and at the moment I´ve got some tartan cushions in position, don´t know which clan though! Green was good too, I agree to that.
Lots of colours go well with brown,my sister has a dark brown sofa,she matched it with a lovely shade of green not to bright not to dark,i went wow when i walked in an seen it and blended the rest of the room around it.