Look for this book -- Grasses: Versatile Partners for Uncommon Garden Design" by Nancy J. Ondra, Saxon Holt (Photographer). It sells for about $16 through Amazon.

The book has lots of incredible photos of ornamental grasses in gardens mixed with other plants. It's also a good reference on grasses. Some plant combinations that stand out include Russian Sage w/ various Miscanthus varieties. Also, Golden Hakone Grass with hostas and other shade perennials. In my garden, I have combined Miscanthus (Adagio) with Russian Sage and Black-Eyed Susans to good effect. Blue Fescues seem to go well with various sedums. I combined Golden Hakone in a shade bed with impatiens, hostas, dwarf iris and a Japanese red maple (Garnet).

verbena bonariensis
any coreopsis, esp. "moonbeam"
small conifers or prostrate junipers
sometimes roses go with variegated grasses (esp. white & green)
taiba, the dwarf mounding shrub (i think it's a pittisporum)
really, there is no end to the possibilities

My favorite is Miscanthus sinensis 'Gracillimus' with Eupatorium 'Gateway'. I saw a show on HGTV that had two gentlemen gardeners from Michigan, and they had a blue spruce tree, quite large, that had a skirt of Pennisetum alopecuroides that was absolutely beautiful. I remember the show was hosted by Erica Glaser (?sp), and they had a maze of grasses that included numerous Miscanthus, which looked so neat together. Anyone recall that show?

Well, all the suggestions here are good. You really cannot err, especially if site (cultural) requirements of grass and perennial are similar. Stare at the grass, close your eyes, andÂquickÂwhat color do you see? Texture? Relative height?

a. Pale, delicate, short? Coreopsis 'Moonbeam.'
b. School-bus yellow, coarse, taller? Black-eyed Susans. Get the picture?

My favorite book, for what it's worth, is Piet OudolfÂs Designing with Plants, an inspirational book that focuses on light, color, texture, shape of (less common) perennials that happen to combine well with grasses.

Here is a link that might be useful: Designing with Plants