I can never get enough of these:
4Mat "Back Again"
My favorite chiptune to this day. I can't really explain why... it's one of the first I heard back when I started listening to this stuff, and it's really catchy. I also used to load it up into Milkytracker to see how he made it, and it gave me a new level of respect for the limitations of Amiga tracking (I'm pretty sure it's an Amiga mod).
https://www.youtube.com/watch?v=k4QKOsqLJRg
Strobe and Ampli "Chipset Sunset"
This is also one of the first chiptunes I ever heard. It was in a compilation video of chiptunes in which each track's details (module type, channel number, size in kb) was listed. I thought ".XM" was some bizarre chipmusic programming language or something... this is when I was mystified by the whole process of making this music.
https://www.youtube.com/watch?v=RDY21um7x4o
Joule and Ko0x "Caroline in Neon Hot Pants"
This one I first heard in a different compilation of chiptunes, when I was starting to get a handle on how to track, etc. So damn catchy! And the attention to detail in the phrasing of the lead instruments is great. Can't tell you how many times I've had this stuck in my head or broke into an acapella of the main melody.
https://www.youtube.com/watch?v=tRCZ8l4pAk4
There's so many others I love too...