Yes, some laser rangefinders have a slope determination mode built right in.  The Bushnell 1600 w/slope, and the Bushnell Tour V2 w/slope both have this feature.  The feature will actually measure the degree of slope and display that slope under the actual yardage.  For example, if you had  4 degrees of up-slope it would show +4 and the effective yardage.  The actual yardage displays above and the effective yardage will show below.  So if you have an up-hill shot of 165 and a +4 slope, the golf rangefinder would give you the effective yardage to the uphill target.  In this case it would be about 178.  So you are equipped with the actual and effective yardage.  You then select a club for the effective yardage.  With this device you will never need to wonder which club you should pull on an extremely up-hill or down-hill shot.