Profh0011, IRON FIST is an early Byrne title I have a special attachment to.

I also like some of Byrne's earliest work. The first I purchased off the stands of Byrne's work was DOOMSDAY PLUS ONE # 1, which I still find very entertaining on re-reading.
And the ROG 2000 strips, in E-MAN. Which I first purchased in the 1981 Pacific comics reprint edition, in b & w.
SPACE 1999 also has some nice Byrne artwork, and painted covers.
But IRON FIST is the series where you can really see him develop, from 1975-1977. (And the IRON FIST storyline then continues in MARVEL TEAM-UP 63-64, and in POWERMAN/IRONFIST 48-50)

I especially like AVENGERS 181-191, as much for the Michelinie scripting as for Byrne's art. And Byrne has a huge range of inkers on this 11-issue run. I especially like the first issue, outstandingly inked by Gene Day.

But as you say, Prof, there are many other series I remember fondly. Some of the best were just single issues Byrne did, such as MARVEL TWO-IN-ONE # 50.
And also MARVEL TWO-IN-ONE # 43.
And HULK ANNUAL # 7 (1978)
And MARVEL PREVIEW magazine # 11 (Starlord)
And the two-part MARVEL PREMIERE story (Antman) in issues 47 and 48.
To Name a few.