A B737-400 Flight Crew encountered asymmetric flap extension on final approach.

Narrative

Turning base to final for a visual approach to the runway; the First Officer called for flaps to 25 and then to flaps 30 in order to finish landing configuration. When I selected flap handle to 25 and then to 30; noticed that the flap gage indicated asymmetric flaps between 15 and 25. We broke off the approach and flew out to the north of the airport where I ran the QRH for this flap problem. I notified Operations and Dispatch of the problem and also relayed our intention to land at our destination with the flaps non-normal. I then briefed the Flight Attendants and the passengers.An emergency was declared with approach and CFR equipment was called to standby. The QRH items were finished and the approach was commenced again with the First Officer continuing to fly while I performed the pilot not flying duties. Aircraft landed in a flap 15 condition with adequate runway length available for the condition of the aircraft. Touchdown was around 154 KTS and a normal rollout proceeded.I took the aircraft at 80 KTS and turned off at the end of the runway and taxied to the gate where the passengers were deplaned. Dispatch and Maintenance Control were called to coordinate repairs to the aircraft.