I'd like to paint our cinder block wall but wanted to smooth the surface first. What are my options besides installing sheetrock on a wall?
You could use an epoxy coating (similar to what you use on a garage floor) - they are thick enough to give a smooth coat on cinder block. You would need to first morter/plaster the seams to get them smooth. There are also concrete compounds intended for use on vertical structures (see concretenetwork.com for examples) - that can give a very nice appearance.
Plaster or sheetrock would be quite a bit less expensive though.