I just learned how to set cursor theme for X. Xcursor themes can be found in /usr/share/icons/ or (per user) in ~/.icons. A strange place to put them, but whatever. One can set their cursor theme of choice by adding the line Xcursor.theme: Theme-Name to their .Xdefaults file, where Theme-Name is the name of the folder containing the theme.

Themes can be downloaded from the official repos or from other sites. Do a pacman search for xcursor and a few themes will pop up. If you want the mouse theme to apply to all existing windows, you'll have to restart the programs. For me, this means I have to exit out of X (which kinda sucks, but whatever). If you want the XCursor theme to apply to newly created windows, just run xrdb -merge ~/.Xdefaults.

Right now I'm just rockin' a white mouse theme called Vanilla-DMZ from the repos. Suh-weet.