Was just reading your post on the Not About Food board and wanted to make a couple of recommendations for some Mexican restaurants we like. (We tried Sierra's and didn't go back.)
In Chatsworth, 2 blocks past Topanga Canyon on Devonshire is Los Toros. For more information and their menu, try www.lostoros.com - enchiladas and chicken hard tacos are my favorites (chips are served with salsa and a warm bean dip just to warn you.)
In Agoura Hills (located in the Vons/Sav-on shopping center on the SW corner of Kanan Rd. and Thousand Oaks Blvd.), we keep going back to:
Cilantro Mexican Restaurant
5617 Kanan Rd.
Agoura Hills, CA
Service is great. Drink refills and chip/salsa refills are prompt, and menu recommendations have always been on target. Even brought me a sample of a soup so I could try it before getting the whole bowl.
When we lived on the Westside, we often frequented Gilbert's for their very cheap breakfasts. I think I'm among the minority on this board who like La Serenata Gourmet. I won't eat at the El Cholo in Santa Monica, but made the trek to the original location on Western often enough (even from the Valley.) I'm also a fan of Paco's Tacos in Westchester for what it's worth.