Take apart an optical mouse

Step 5 Easily Desolderable

Some components are more easily de-soldered from a PCB than others. Through-hole parts with three pins or less are pretty easy to remove using solder-wick, for example.

1) Each of these mice has five micro-swicthes; relatively nice SPDT ones that might be useful

2) Infrared emitter and "direction detector" as part of the mouse wheel. In the mouse wheel, which is also optical, there's a two lead part that is an infrared LED, and a four-lead part that is dual photo-transistor or (perhaps) more complex circuit that outputs signals sufficiently complex for the microcontroller to tell which way a slotted wheel (turned with the mouse wheel) is turning. This is all on a nice separate board; with a bit of mechanical skill you might be able to use the wheel separately from the rest of the mouse.

3) The new version of the mouse has a three-pin 6MHz (a common speed for USB things) ceramic resonator hiding under that metal can. (A three pin resonator replaces a crystal and two caps in most microcontroller circuits.) The older version has two 2-pin resonators (somewhat less useful IMO.)