The agaves aren't the only things blooming. Sam identified this plant taking over my front fence as Solandra maxima, also known as Cup of Gold vine.
The first year I lived here this plant grew about 20 feet and now reaches across the whole front of the yard. It has since filled out and is trying to take over the neighbor's yard. I'm going to have to get the pruning sheers out.
Not only does it grow fast but it does it with almost no attention from me. It stays fresh and green all Summer without any supplemental watering. I think I love it for this more than the flowers, which sort of look like burst balloons to me.
It's a little scary how successful it is. I took some cuttings and stuck them in dirt and they have already sent out new greedy little branches. I have bunch if anyone wants some.