I built an alarm system for my work trailer (it's full of tools). It's pretty cool, cell module, gps, rfid, motion activated lighting, basically one of everything from Sparkfun. I used up all the pins on the 2560 and added a 328 and two shift registers for more stuff... OK i'm just bragging at this point, on to my question. I have to run a variety of sensors a maximum of 50 feet (serial, 5V TTL, and 3.3V temp sensors). What would be good wire for this or is it too long of a run? I was planning on using CAT5e (24awg 0.026ohms/ft) or Home Depot sells sprinkler wire (18awg 0.0064ohms/ft) with up to 10 conductors and i don't think they are twisted pair. Or i can get some shielded CAT6. Or could i run everything in metal conduit for shielding. Any thoughts?
Unlike in other situations in life, size here doesn't matter. Almost any wiring you can find will do, the smaller, the easier it is to handle. For what you are doing, the sensors will do just fine with just about any wiring >28 gauge size.
Shielded CAT 6 sounds very good for this. Best if you use the flexible stranded-wire versions, from a vibration perspective.
Home Depot carries 4/24 security wire that would be great for this. Can by as a 500' roll and break up as needed.
I use the same for my fencing club, running +12V, Gnd, Tx out to the remote boxes with a TX return (really just another ground). The 4 strands are surrounded with AL shield also, ground one end (only!) for noise protection if needed.
The 24/4 is stranded. Nice to work with.
I'll definitely stick with the stranded stuff to prevent fatigue. Found shielded 22/4 stranded 500' roll for $84, not too bad. 
Everything on these lines should be well under 200mA per line. The temp sensors are 10K thermistors, i can account for any voltage drop in the software. What is the reasoning for only grounding one end of the shielding?
Ground one end of the shield to avoid ground current running thru the shield, commonly known as ground loops.