Update as of 10/06/09 - Thanks to Pam at Hook Mountain Growers, who suggested I check with the site whatsthatbug.com, we've identifed this as a Spined Micrathena spider (micrathena gracilis). I think I'll call her "Athena Grace." She eats her web every night then builds it again the next day! That is really a terrific site if you're looking to identify any creepy crawlies.
It was tough to get a good shot of this spider, who's been spinning away in the bed in my side yard for the past week. Anybody know what she is?
She's about a centimeter in lenth and has a huge black abdomen with light yellow markings and horns on the front of it.
In this shot, you can see her underside, which is cone-shaped and ridged.
I've tried googling "black horned spider" but didn't find much, so if anyone knows her identity - or of a good site for identifying spiders, please pass it on!