I'm making a crosscut sled for my table saw, and I want it to slide freely. I've read various places that waxing the under side of the sled helps a lot. My question is, what kind of wax should I be looking for? I am not looking for an exact brand recommendation; more of a general idea of what aisle of the store I should be looking in.
"Paste wax" is the go-to wax for your purpose and for waxing tool surfaces.
Avoid buying a wax that contains silicone, because the silicone can directly or indirectly get transferred onto your wood and cause problems when you go to apply finish.
I've also been told to avoid car wax since it can contain silicone and apparently it can also contain abrasives (which seemed odd to me, but I suppose any type of polishing involves abrasives...).
I have very good luck with a purpose-made product called Bostik TopCote. I first saw this product when I briefly worked for an architectural millwork shop. One spray can goes a long way, and it contains no petroleum oils or silicones. I used it most recently on a donated table saw which I reconditioned, after resurfacing the rusty table. It did a beautiful job. I appreciate the slick surface especially when using a sled. I use it on other tools as well, such as bandsaw, joiner, etc. I would not want to use paste wax because I would be afraid of buildup and transfer to the work.
Hope this helps.
You've already tried paste wax and had it work for you, but for future readers who might not have any in the shop already and would like to try it for themselves on the cheap I wanted to link to this previous Answer which gives the method to make it at home (simplicity itself).
Paraffin is the old standby. Works well.
A friend who is a cabinet maker used Bowling Alley wax and his sled slid very well. You can find it on the interwebs, but I think he actually got his from a bowling alley.