Well, I love ornamental grasses and think they offer something a little different than the ordinary landscaping that you typically see.
From a marketing perspective, I try to make sure my property's landscaping color scheme (of annual color) is different than my closest physical competitors. I like to stand out.
Yellow is the first color to be processed by the human eye, so it's always good to have yellow. White signifies cleanliness, so I like to have some of that too. "Undulating" planting beds are more attractive, so I like my planting beds to have a sort of curvalinear (<---Is that a word?) shape to them.
Fresh mulch (if you use mulch) is a must and should be complementary to your building colors rather than to your floral choices. Fern gardens and other perennials are really attractive choices, too.
Don't forget scent either. Try to have some pleasantly scented plants and flowers closest to the door (where your prospects typically slow down as the approach your leasing center entrance). I like herb gardens, too. They offer a nice difference and if you remember to put signage on them, indicating what they are, your prospective residents will see one of your amenities right away when they visit. It helps set you apart from the rest.
I'd suggest trying to do something eye catching. Like cool shapes, spell "home" with flowers or anything in that sort. Now if that is possible is another matter
I agree with Lisa, play with colors, layer them, sometimes one color brings out the beauty in another.
Go to botanic garden one weekend and see what they are using
I don't know anything else that would be better then mulch, maybe landscape fabric with stones on top, but that is both expensive and a short term solution. Why not go green, get some strawberries going which also add some color to the scheme...
I like the look that pine straw gives to a bed area - would not suggest it in an urban setting however. With regard to flowers, I suggest white or yellow Cana Lillies - definitely hot!