Said it once, said it a million times. 3M High Performance Cleaning Cloths, relatively inexpensive (comes in a three pack), washable and very reuseable, good for lots of other things as well.
The cloth itself will not scratch surfaces with normal pressure (of course, anything will scratch a surface if you apply enough pressure, that's a variation on Fudd's First Law) however, any particles picked up previously can so keep them clean.
No cleaners or fluids are required though for very stubborn crud, a solution as noted above applied carefully with a cotten swab can be effective.
The High Performance Cloths are generally available at most any large supermarket or drug store.