Rather than a cowboy, Woody was originally supposed to be a ventriloquist's dummy, but luckily, executives at Disney had the good sense to point out that ventriloquist dummies are actually terrifying and that Woody should probably be something less nightmare inducing.
Likewise, rather than a cowgirl, Jessie (who was introduced in Toy Story 2) was originally supposed to be Señorita Cactus, a sidekick to the Prospector who was "to sway Woody with her feminine wiles."
In original drafts of Toy Story, Buzz Lightyear was instead Tinny, the main character from Pixar's 1988 Oscar-winning short film Tin Toy. Deciding that Tinny was too antiquated, the character morphed into a G.I. Joe-esque action figure and later into a spaceman, first called Lunar Larry, then Tempus, then Morph, and finally Buzz Lightyear as a nod to astronaut Buzz Aldrin.
Though Woody later became the good guy we now know and love, his character was originally supposed to be kind of a jerk. In his book Zig Zag: The Surprising Path to Creativity, creativity researcher Keith Sawyer mentions that the first drafts of Woody had him abusing slinky dog and pushing Buzz out of a window, but it was later decided that Woody should be a more likable character and that Buzz should fall out of the window by accident instead.