Thanks for the plug, Donnie!
Aside from some of the 24-hour joints like TeeJaye's (I think all of them are 24/7), Buckeye Donuts, and Waffle House, it's hard to find things that are open super early. Like someone said, Breakfast Barn and Tommy's open at 5:30, but the closest thing to SN/downtown is probably going to be DK Diner. They have a solid diner breakfast, plus some of the best donuts in town.
Most other spots open by 6:30/7: de-NOVO bistro & bar (an under-appreciated bfast, IMO), Cup O' Joe downtown, Danny's Deli, Lexi's on Third, and Jack's Diner open at 7, as does Tasi in Short North. In the Ohio Union is Sloopy's Diner, which is basic but kinda fun, also open at 7.
I know there's been a lot of talk of a 24-hour diner in Short North. I think Liz and/or Tim Lessner have talked about opening one. That would be a dream come true for me.