I'm a perennial gardener more than anything; I rarely buy annuals, except for container gardening. But this is a great time of year to buy annuals; most nurseries are running specials (2 for 1 etc) before the real heat comes and it's too hot to plant. I put together a container today including zonal geraniums 'Tango Orange' (isn't that a great color?) and Nieremburgia 'Mont Blanc' among others.
I use a good, organic potting mix and fill the container to approx. half full: