When the LA chapter went up to the Santa Barbara Wine Futures Event, we tried the 2007 Jaffurs Petite Sirah... that was one of the best I've ever had.
We also tasted a couple of solid examples back in May when Emily grilled us up some burgers. The 2005 Michael-David "Petite Petit" drank nicely with a big beef patty fresh off the grill.
I find it's much harder to find a bad bottle of it than a good one. Also I think they've annoyingly started spelling it "Petite Sirah", which is lame. Even something as simple and inexpensive as the Bogle is pretty solid ($12). I don't think I've ever had one I've actively disliked though.
Petite Sirah had the "honor" of being my favorite varietal for awhile. I agree with Andrew's sentiments on finding bad ones--I haven't had too many domestic ones that I've disliked. I recommend the website PSILoveYou.org, it's supported by a myriad of P.S fans, so take that with a slight promotional grain of salt but these folks really do love the grape, and there is a section that has a variety of links to Petite Sirah independent reviews and info.
My first love was the 2001 ConCannon Petite Syrah. Recent vintages weren't quite as tasty to me. Recently, I've been enjoying the Consilience La Presa Vineyards releases. I also like the SBC, too, though I think they may only be selling magnums of whatever release is current, right now. So make sure you're extra thirsty.
I think I have a bottle of that Jaffurs on my rack actually...this has motivated me to open it soon!
Wolff Vineyards in the Edna Valley and Penman Springs in Paso Robles are two of my favorites in this category. Silkwood makes a wonderful PS but at $48 is a bit pricy.
Consilience La Presa Vineyard Petite... 2005 will blow your mind. If you like um big ultra rich bursting with blueberries and white pepper. Delicious, and yes, I am biased.