Lorna Sass's Cooking Under Pressure (Wm Morrow, 1989, 2009) was her first pressure cooking book and certainly a classic, but her later Pressure Perfect (Wm Morrow, 2004) is the one to get. She had learned all kinds of new tricks by the time she wrote Pressure Perfect.
Lorna's absolutely sound on methods, but her palate is a little bland. For deliciousness, turn to Victoria Wise's The Pressure Cooker Gourmet (Harvard Common Press, 2005). I don't know why Victoria isn't tremendously famous -- not one of her books is indexed yet. She has tremendous breadth and a perfect-pitch sense of recipe construction. Give her a try, you'll love her.
[How do I put my picture up, the way you guys have? When I look at my Profile information I don't see uploading a picture anywhere.]