Based on a previous poster's recommendation, I tried El Salvador Con Sabor at 5105 Venice Blvd, 4 blocks west of La Brea. It is in a strip mall and they have yummy pupusas of many different varieties made fresh to order.
If you take the 10 East to the La Brea exit (NORTH) it is a very short drive from West L.A.
Their number is (323) 936-0231 and do take out too. Good luck on your pupusa hunt!