When I'm indoors or want a slightly closer perspective, then my next most used lens is the 50/1.8 lens. It is also great for the budget-minded, being only around $200, so I would also recommend it to anyone as a good starter lens!
On cropped bodies, my most used lens is usually around 50-55mm, so near that of the 85mm field of view on full frame cameras. One of the most affordable of these at only around $200 is the 50/1.8. It also works on full-frame, so if you're thinking you want to invest in full frame in the future, this is a lens you can keep for the long haul.