I am looking at a '64 for my girlfriend. Aside from the usual stuff, are there any special places of concern to look for? I know every car has its own problems spots, where i the '64's? Hidden areas for rust?

Up here in rust country (MN), the usual places to look are:
Lower corners of windshield and rear glass
Rear Wheel lip
Rear Quarter extension (behind wheel opening)

How about the back of the car below the trunk lid lip, between the taillights?

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Make it the way you like it, forget what the other guys say!
http://chevelles.com/showroom/alelcaminofront.jpg
http://www.angelfire.com/al4/alcamino64/index.html

Other places I would look are the trunk (make sure you lift the mat and check from underneath as best you could) and trunk extensions, inner and outer rear wheel wells, also the front passenger inner fender under the battery. Check that area and make sure it hasn't rotted more than just the batt. tray. Other than that 283 and John D have most all else covered.
Steve

Another thing to keep in mind is that if you're going forward, rain travels UP the windshield, driven by wind. My '72 is from the rainy part of Oregon, and the metal along the entire upper edge of the windshield had holes big enough to put my thumb through. I don't know if this applies in your case, but the upper edge is a good thing to look at. However, most of that channel is hidden. Look for hints of rust above and below the windshield upper trim, and on the front edge of the headliner inside. The only way I knew there was a problem on my chevelle was water dripping onto my lap while driving in the rain - I removed the upper trim and pulled back the headliner and could look down onto the seats from above the car through the holes. Serious rust, and it was invisible until I took it apart. Good luck!