They have the best prices I've found on pots, power jacks, and enclosures. Their prices on resistors is basically in line with everyone else's.
They basically just sell the 4Site catalog.
I bought some of those aluminium-center knobs from them, and their were awful. The hole size was inconsistent, and not even always centred.
Pedalpartsplus is still mah favourite. They have UV LEDs. Which I tried to buy at Mouser, but they had some warning about cancer, so I keep buying them at PPP so it's not my fault.

They also custom drill screen print, etc. And they sell 50 cent jacks that are actually pretty nice (they're also smaller,which is nice for tight builds). And they sell Panasonic ECQ-Vs for the same price as Mouser. Oh, and they'll ship first class mail so it'll only cost you about 2 bucks if you forget, like, one thing.
Smallbear rules for a lot of things too! They sell tools and stuff. Good stuff! For pretty decent prices!
If these smaller stores keep popping up, I might be able to stop buying from Mouser! ... but not yet.