Yet another 1 who thinks buying lens can give the desired effect without knowing even the very basics of photography.
Do more homework, all the info are within few clicks away, this is especially useful for people who are on very limited budget.
That aside, how do you even define a "good" DOF?
Large DOF is "good" for landscapes while thin DOF is "good" for portraitures.
Any prime between 28mm and 35mm will be ideal for an all purpose lens and from my short eperience in Pentax, I am certain Pentax has the best range of such lenses for cropped bodies. If you can afford, the FA 31f1.8, otherwise the best value for money DA 35f2.4. In between you have the F28f2.8, FA 35f2 and DA 35f2.8 macro. There are more choices if you don't mind manual focus. I like this particualar focal length range because you can go closer to your subjects as most of these lenses have a short MFD. When you shoot close to your subject, you can get good blur-off back ground transition, like some of my flower photos I shot with my FA31f1.8. It's MFD is 25cm ( 1 foot) and after 3 months, I still don't have enough of this lens and it's stuck to my K5. No other brand has such a range for their cropped bodies.