This spectacular agave above -photo (copyright © Julia Etter & Martin Kristen) from http://www.rarepalmseeds.com/ - is an unpromising infant when viewed in a 4" pot, which is what local nurseries are likely to carry. But agaves grow quickly with water. It would be worth the time to grow it into giant pot size.
The Rare Palms site has seeds of all kinds of amazing agaves, yuccas, bromeliads and cyclads. This is the season for starting cactus and succulents from seed. The seeds "know" when it has rained.
There's a place for aloe seeds as well http://made-in-afrika.com/aloes/dichotoma.htm with pictures of aloes in their native heath. Aloe thraskii (South Africa) from the coastal regions grows easily along our coast as well, I've seen it planted in a group of three each 15 feet tall, lording it over the landscape.