removing glue from felt pads on chair legs
If the glue is still tacky at all (or ever was), Laquer Thinner or "Goof Off" may be a good solvent.  If the glue is a hard type glue such as Elmer's or a Wood glue, your best bet is to try to chip off as much as possible with a sharp pocket knife. Then a block sander or electric sander may work OK for the rest.  Or if you have access to a flat bastard file ($4.99 or so at Sears Hardware or Home Depot, Lowe's, etc..), then you can really put some muscle into it.