There are plenty of decent sit-up benches on the market. If you are serious about core training, you may want to invest in a bench that offers more though. The Finer Form Semi-Commercial Sit Up Bench is ideal for core training. It comes with a reverse crunch handle and has 4 adjustable height settings for decline sit-ups.
This bench has 3-level adjustable rollers. It has max weight capacity of 660lbs.