I highly recommend Adafruit Industries as a supplier of electronic components.
Her site (I think of the store as a “her” so, that’s the pronoun I’ll use here) promotes education and creativity in the field of electronics especially for women, young people and artists. However, it appeals to me a great deal too and I’m not in any of those categories.
One time, I ordered a bunch of parts from her and after putting them in the robot, I thought one of them was defective. I posted on her “help” page with info about the problem. She handled my case very politely and sent a replacement part free of charge. A couple days later, I found out I WAS WRONG! The part wasn’t broken at all! Maybe I’ll send a couple of customers her way and make up for the money she lost…
Whenever I need a part, I’ll always check Ada first and if it’s on her site, I’ll buy it from her – no doubt.