Lately I've been studying a few of Piet Oudolf's garden books. His garden design philosophy has been described as "naturalistic", as he uses mostly perennials that look close to their wild ancestors and that have long seasons of interest. His gardens are gorgeous - let me repeat, GORGEOUS! - and best of all, many of the plants he regularly uses in his designs do well in Calgary - a bonus!
I'm planning to write a little more about his design principles here in the next few months, and maybe even an article for the Calgary Horticultural Society's newsletter (I'm getting ambitious, aren't I?) But in the meantime, have a look at some of these photos posted on other websites. I could spend all day staring at some of these, couldn't you?
Piet Oudolf interview on Gardening Gone Wild (with lots more links in this article)