I travelled to the second half of this year's Tour, picking it up in Ax les Thermes all the way back to Paris, with a company called Bikestyle
. They're based in Australia, but they have about eight years experience running tours to the Tour, Vuelta and Giro. Some of our guides were former pros who'd actually ridden the Tour.
One thing about going to the Tour is you actually see LESS of the race than watching it on OLN. But the scenery is wonderful, the atmosphere is amazing, and being able to ride up Luz Ardiden the morning of Lance's heroic climb, or sprinting past the gendarmes into the finishing straight at Maxient St l'Ecole, cheered on by crowds already five or six people deep along the barriers are memories that will last a lifetime.
There are plenty of tour companies out there doing tours to the Tour; Velosport, Velo Echappe, Steve Bauer, Trek, Sporting Tours, Butterfield & Robinson. Do a Google search. Some are more expensive than others, some are more experienced than others. Decide what kind of a riding/viewing experience you want. Do some research, seek out testimonials in forums like this. Have fun!
Oh yeah, and get started soon; our tour was quite large, but already had a waiting list by October, and with Lance going for six, interest next year will probably be high.