Chris Huelsbeck, of course! He was great both on the C64 (R-Type, X-Out, but also
Dulcedo Cogitationis and
Starball in my opinion) and the Amiga: the Turrican series obviously, as well as Apidya, Z-Out, and R-Type again (different, but equally great, music).
Laxity, especially
"The Alibi", one of the great SID tunes.
Talking about Tim Follin, one must absolutely cite the music for
Agent X II and
Scumball, among others.
Other favorite game music:
Rubicon by Jeroen Tel and Reyn Ouwehand
Zamzara (hi-score/ending) by Charles Deenen
Gaplus, Savage, Tomcat by Jeroen Tel
Street Cred Boxing by Johannes Bjerregaard
Martin Walker, Thomas Detert, Steven Diemer, Jens-Christian Huus and Glenn-Rune Gallefoss are other great composers of SID music.
ggf162: Pretty much everything from VVVVVV
Yes, especially "Pressure Cooker" and "Potential for Anything".