A solution would be to configure a DHCP static lease, if your router allows it. I like this solution because I can set all of my connected devices' IP address and DNS configuration in an unique place.

1. In a terminal on the Raspi, run the `ifconfig` command to know its MAC address (HWaddr **XX:XX:XX:XX:XX:XX**).
2. Open your favorite browser and enter your router's IP address. Probably 192.168.0.1 or 192.168.1.1.
3. Look for the DHCP static lease option. In the example [here][1], the "DCHP Reservation" button.
4. Enter the MAC address you picked up in the first point and associate it with the IP address you want to. Click [here][2] to see an example of the web interface.
5. Restart the RPi to make it get the IP address you just set up.

  [1]: http://networkoverload.com/routers/linksys/WRT610N.2.00.00.php
  [2]: http://www.networkoverload.com/routers/linksys/WRT610N.2.00.00/DHCP_Static.htm