Slide rules have come in different formats over the years. The most familiar is probably the  3-part model with a fixed outer frame and a sliding inner rod, and a sliding clear window with a reticle line etched into it for aligning numbers (the cursor). While far from being any type of "collection," I do have a couple nicely preserved models. The ones from Keufel & Esser (K&E) are at the top of the table below. The Beginner's slide rule model is very basic with graduations on one side and some conversions on the other. The best of all is the Pickett N600 ES Log Log that is in new condition and actually still has the box, leather case, instructions and certificate. The   Pickett N600 ES is the slide rule model that went to the moon with the Apollo astronauts (not the one I own, of course).

Finally, a few of the cardboard calculator I have are at the bottom. Probably only the VSWR Calculator from M/A-COM can be considered collectible. My good friend Patrick Fitzgerald bestowed it upon me when I went to work for him at General Electric right out of college. I can recall some of the older engineers still using slide rules there when I arrived in the 1980s. In fact, the first algebra textbook I had in a community college right out of high school in 1976 had a section in it on how to use a slide rule. The Sterling 684 plastic slide rule that I bought at the bookstore is show below. Shortly thereafter, the HP-35 hit the market and the world changed forever (now that was truly a disruptive technology).

Here is the definitive source: International Slide Rule Museum
      Slide Rule Library Archive of books, manuals, instructions and ephemera
      Instructions on how to use a slide rule
Or, try the Slide Rule Guy

Visit the Oughtred Society (William Oughtred - inventor of the slide rule in 1622)
Buy new-in-the-box, mint condition slide rules
Here is a website on vintage instruments (slide rules and other instruments of math, drafting, science, and music)