To create a realistic sketch in Photoshop you need some pencil sketch textures or better still you can use pencil drawing brushes. In this list I have gathered some of the best pen and pencil Photoshop brushes that will allow you to create different digital drawing and painting effects. These drawing and illustration brushes are a must for all the digital artists; especially for the ones that use often graphic tablets.
Photoshop is a great tool to create realistic sketches, but to do so, you need the appropriate photoshop brushes. This website has a collection of links to various realistic looking pencil burshes that will help you to create pencil art using Photoshop.