Have a look at the Lensbaby Composer (update: discontinued): It has an unique feel to it, has been used very effectively by wedding and portrait professionals for a long time. Now replaced by the Lensbaby Composer 2, quite a bit more expensive.

At ~$300 for the Canon EOS mount version, it isn't cheap for a lens that isn't really general purpose at all, but for sheer creative possibilities, it is unmatched.

At a much lower price point, some very striking portraiture has been done by simply stretching a single layer of the finest available black sheer nylon stockings, with or without a strategically located hole in the material, over any lens you have, and using the resultant partial soft focus to powerful effect. This is especially useful to tone down beard stubble, harsh wrinkle lines or double chins.

Some studio photographers use very long telephoto lenses (300mm, 500mm) for portraiture: The angles and structural curves of faces appear stronger and better defined, and depth of focus can be finely tuned for interesting effect. Using a tele with a very deep DoF gives an almost 3-dimensional feel to very tightly framed portraits - You would need lots of light, though, to cope with the really narrow apertures required.