Camel Spiders are real, but they're not spiders. They're solifugids, another type of arachnid. They get quite large, but not as big as they apparently look in many email forwards, which are optical illusions caused by holding them close to the camera.
As for the biggest spider, it depends on what you include. If you only count "true" spiders, the tarantula (a mygalomorph) does not count. It would likely be something from the nephila or argiope groups of spiders. (I believe in North America, the largest is either Argiope aurantia or Nephila clavipes, common spiders)