A lot has been written about guitar pots but almost everybody agrees that the most used guitar pots in quality guitars and basses are made by CTS and Bourns.
Potmeters for single coil pick-ups and humbuckers
For guitars with single coils 250kOhm pots are used most of the time. For humbucker guitars 500kOhm pots are common.
Potmeters for volume and tone control
For volume control it is common to use logarithmic potmeters. These pots are marked with A, AUD or LOG on the back of the housing.
For tone purposes lineair pots are often used. These pots are marked with B or LIN on the back of the housing. Logarithmic pots can also be used for tone control. This is basically a matter of taste. Find out what you prefer by experimenting a bit with different pots.
Gitaarpots: short, full-size of long?
For pots direct mounted to a pickguard you can use the short version although the full-size version will also fit in most cased. For carved top guitars you will probably need the long version pots. The pots have a longer shaft needed to mount for mounting to a thick carved top.
Next to these guitar pots in different sizes we have variuos push-pull pots available. This is basically a potmeter with a switch attacted to it. The switch can be used for various pick-up wiring options adding lots of tone options to your guitar.
Lots of wiring diagrams can be found online but this book on wiring diagrams is highly recommended.
GuitarSupplies stocks a wide variety of both CTS and Bourns guitar pots.