I personally use the 85mm f/1.8 as my portrait lens. It works beautifully at all apertures, even wide open, and the range is just perfect for me because I like doing chest up shots. And physically it just looks like a beast, and it's nice to un-mount it and compare the sheer massiveness of the rear element to any other lens of less aperture.
Here's two of mine I personally love that were taken with this lens. They aren't exactly what you'd call a "portrait", but they're close enough and it shows the awesomeness of this lens. The brokeh is absolutely stunning even stopped down as these two were.
Canon Rebel XT, 1/800 second , F/3.2, 85 mm, ISO 200
Canon Rebel XT, 1/250 second , F/5.0, 85 mm, ISO 200
All-in-all, I Highly recommend this lens.