[dazee]

For my main track before I tore it down I was using the 3du5c photo sensors and some little automotive LED bulbs in the overhead gantry - these were not of course powered from the arduino as the current draw exceeds the output of the arduino pins.  But you can still tap into the same power supply you use to run the arduino.

But you can use really anything that will return a basic high/low value back to the arduino.  I have also used the uxcell Slotted Light Switch sensors which are basically the same as what you have linked, but in a package you can mount in the track so you don't need a gantry - not really suitable for plastic tracks though as need alot of work to fit them.  Best for routed tracks.

Currently on my little test track I am using lasers as wanted to get triggers at multiple points and did not want multiple gantries.  And you know.... lasers!!! 

With the 15v power supply you also have the option of adding some of those little voltage adjustment circuits you can get that will allow you to tune the voltage independently for each lane and account for cars that run better on your track at a lower voltage.  These circuits typically drop your input voltage by 3v in order to run, giving you an output from 0v-12v