MostlyGeek

Use this command:

systat -ifstat 1

It will show something like this:

Interface           Traffic               Peak                Total

      lo0  in      0.000 KB/s          0.000 KB/s            7.635 KB
           out     0.000 KB/s          0.000 KB/s            7.635 KB

     bge0  in      2.090 MB/s          3.439 MB/s            2.263 GB
           out    36.603 KB/s        173.008 KB/s          343.683 MB

     fxp0  in      2.503 KB/s          2.430 MB/s            1.137 GB
           out    99.174 KB/s        509.109 KB/s            2.078 GB