Any recommended 24 VDC shields that plug directly into the Uno?
Are you talking about powering the UNO or controlling 24 volts?
I am looking to manage 2 24 VDC inputs and 1 24 VDC output using the Uno. If I have to go to a different Arduino model, I am certainly willing to do that
Manage, as in select one or the other to connect to the output?
Under Arduino control? Use a SPDT relay, Common as Output, NO & NC connect to the inputs. Coil controlled by Arduino. Or use two relays if you need to have both disconnected for some reason.
Or let the higher of the go thru always? Diode isolation find a couple with high enough current carrying capability and reverse voltage that can take 24V.
How much current? This Uno shield I offer can be populated with just 2 relays and used as I described above. 5A limit on current tho.
http://www.crossroadsfencing.com/BobuinoRev17/
Or a standalone version
I think OP just wants a voltage divider for the ~24volt output of his laser gate.
http://forum.arduino.cc/index.php?topic=381263.0
A 22k resistor from sensor output to a digital input, and a 5k6 resistor from the digital output to ground would do.
Leo..