I was once working on custom-ordering a shirt with the Quote form my Avatar on it...
I can also picture a graphic black skeleton-silhouette on a green background with two silhouette figures in white attached to it; "iDinozombie"
Or do a variation on the Jurassic Park film Logo that reads "Jurassic park; Chicago Edition"
Or an 8-bit purple monkey with bat-wings and a super-mario style fireball in each hand. And on the back use the old style Ninetendo Oval Logo with "Dresden Files" instead of Nintendo and the words "NOW you're playing with Power!"...though there will likely be copyright issues with that one so...
A picture of battered, blood-stained Murphy in combat threads with Shiro's Sword glowing in one hand a smoking P-90 in the other and the phrase; "Go ahead, call me short again..." on the back.
Michael in his Surcoat with a Carpenter's tool-belt sword propped point-down and held with one hand and the other wielding a Claw-Hammer in the other and the phrase; "Multi-tasking for the Lord..."
A battered and bruised Harry sitting on top of a pile of dead enemies with a smoking staff in one hand, blasting rod in the other and laid across a knee and a shit-eating grin on his face and the Phrase "I'm sorry, I can't hear you over the sound of how awesome I am."
A graphic of Hugh Hefner with his head replaced by Bob's skull and flanked by Susan and Murphy in bikini's with the Phrase "Chicks Dig Bald Guys"