Before you read further, know that I'm not just sitting here picking things apart. XD I'm going based on my own current skill level and what I've seen already available.
To both of you:
Scars have been done several times. Don't get me wrong, a realistic scar would be nice, but I know I'm not that skilled yet. XD
Hugrf:
I actually do have a clothing marking I made, but never released. Thanks for the suggestions. :3
Silverball:
I really like the ice marking idea. I may actually be able to pull that off. :3
No promises on complex swirls. XD Not only does FH already come with a set, but other people have done them.
Super hero mask is cute, but I prefer more functional markings.
Please define what a "solid swirl" is?
The mustache has been done already.
So have lines coming from the edge of the mouth.
A lot of realistic animal markings, blur and all, are already out there.
Detailed scales have been done.
Fairly sure I've seen cartoony stripes (and there are several in my own markings pack, as well XD).
Tiny hairs of color may or may not be something already done. I keep imagining the Brindle marking I've seen.
Feathers have been done.
I like the leaf idea. May make a set for that. :3
Thank you both for the suggestions! ^_^ This was actually very helpful. And as for linking the topics, the new markings (when I get the chance to make them) will be located in my already existing Custom Markings thread, as seen in my signature.