My comic has three volumes of custom soundtrack now, that I wrote myself.
Volume 1
Volume 2
Volume 3
I mostly do it just to learn and practice - I wouldn't call it my best work, but I do really enjoy making it.
Some music I'm a bit more proud of though would have to be this. During 2020 I wrote one piece of music each month for a comic I found that I enjoyed. But, by the end of the year I'd composed some 20 pieces, instead of the 12 originally planned. So, I wrote original music for 16 different comics as part of that project. They're all really excellent, and I'd definitely urge anyone interested to give them a listen!