For metal parts, some basics would include a drill press, bandsaw, and possibly a shear or brake if you're working with sheet metal. If you're lucky enough to have a bridgeport or a small cnc then you can really open up your capabilities as far as geometric complexity.
On the plastic side, the above drill press and bandsaw are staples along with a sanding machine. You should really look hard at a 3D printing system or laser cutting and engraving machine depending on your part geometry. These machines can start at the cost of a high end desktop or laptop which has allowed a huge pool of new customers into the market just in the last 5 years or so.
Have you made some investments in equipment recently? What tools and machines did you invest in and why? Let's discuss and I'll dive into more of what a typical full service shop looks like and can offer its customers.