Many of my characters started with the thought "I want to play a character with a powerset like 'X'" (where 'X' was some existing superhero or even non-superheroic character)
BluePulse (Elec/Elec/Mu Blaster) was a bad take on one of my tabletop characters (he should really have been a MA/SR/Mu Scrapper, but side-switching didn't exist when I created him, and I didn't know about Epic/Patron pools yet anyway).
Dr. Bodog (Robot/Storm/Mace MM) and Thunder Glove (Elec/Invuln/Energy Brute) were takes on Dr. Sivana and Black Adam (though TG eventually got his own backstory). Gravity Hold (Gravity/Elec Dominator) started out as Sinestro. Ms. Stungun (Energy/Energy/Energy Brute) was an evil Ms. Marvel (in her classic Silver Age costume, no less, but with an "evil" color scheme - instead of heroic reds and blues, I used greens and purples).
When the shutdown was announced, as a mild form of protest, I made alternate costumes for each of those characters based on the original (so Bodog got a Dr. Sivana costume, Thunder Glove got a Black Adam costume, and Gravity Hold got both a classic Sinestro costume and a Green Lantern costume), and I'd walk around in them. Never got generic'd, because by then I don't think the GMs really cared.
Not all my characters were based on existing characters. Some I just started with a powerset or powerset combination I wanted to play. Sgt. Greenstone was my first Tanker, because I wanted to try Stone/Stone. Diamond Clarity was my final Dominator, because I wanted to try Earth/Ice (she was originally Earth/Earth, but I wanted more ranged attacks in her secondary, so I rerolled her).
And then some just slipped over the line on their own. Dark Eidolon (Staff/Dark Brute) was another case of "I want to try out these powersets" and wasn't intended to be based on anyone, but while I was struggling with a costume, I looked to the Internet for inspiration, and there was
Wraith, so jet-black skin and a trenchcoat it was.
Of course, in my saved-but-unused pile I have lots of copyrighted costumes, from well-known characters like Superman, Batman, and the entire Marvel Family, to obscure characters like the Whizzer, the Black Terror, the Golden Age Blue Beetle (with the chainmail armor), and even advertising mascot Captain Tootsie. I never planned to use them, but I just made the costumes to see whether I could. (And CoH's costume creator was so good, nine times out of ten, I could)
Sadly, no pictures.