I've started buying myself flowers on a semi-regular basis. They're one of those nice touches that make a house feel more like a home, which is especially lovely now that I happen to live and work in said home.
I always just go for a relatively inexpensive bouquet of something seasonal, and often supplement it with clippings from the yard to fill it out and make it special. Winter is my favorite time to do this - the evergreens really pop against any color, and add a lot of interesting texture. In this case, I bought a really small bouquet of white spray roses, and added holly, twigs, and cedar boughs. Double bonus!: they make it look like I've decorated for Christmas more than I actually have, and they make my little office-corner smell like a forest.
In the summer, I love adding things like huge, shiny magnolia leaves and tall grasses; here's an example. Obviously, twigs are always in season.
(I think this post sounds really Martha Stewart-y.)