The problem is that to get a shot in F1 you can't be crap, no matter what a lot of people like to think, particularly with the lack of testing these days, you have to have shown potential at least. Quite simply you wouldn't get your super license otherwise. Anyway, a few that could fit the bill...
Kamui Kobayashi didn't do much in the lower formula, arguably only got his first F1 shot because he was Japanese, he's pretty damn good.
Maldonado, I know he did win GP2, and in fact won more races than anyone else has, but in a relatively week year, and in his 4th season. Most drivers don't stay in GP2 that long, they either progress to F1 earlier, or move off somewhere else, either Indycar, or away from open wheelers all together. I'm far from his biggest fan, but he's done surprisingly well considering his pedigree, well, when he's not using his car as an offensive weapon that is.
Damon Hill, admittedly he didn't even start racing until his mid 20's, and for that reason alone I consider his ability hugely underrated, but to say he hardly set the world alight through the lower formula would be the understatement of the century. Just go look up his record, it was pretty woeful. Having said that one of the main reasons for his lack of results was his total lack of money, he might have been a Hill, but he had it very tough through the ranks. Eventually he got a go testing for Williams at the ripe old age of 31, back when they were able to trial loads of youngsters, the name helped here a bit, and he impressed them mightily. He's generally regarded as having been pivotal in making the FW14b the crushingly effective tool it was. Not to mention then going on to win the title, and come runner up twice and 3rd once, and to win in a Jordan, and to nearly win in an Arrows. Incredibly impressive stuff for someone who literally did next to nothing in the lower formula. He was just shit hot in an F1 car.
Oh, Michael Schumacher. He didn't do an awful lot in the lower formula, admittedly most of what he did was fairly impressive, but the Mercedes driver development team, or what ever they called themselves back then, thought Frentzen was the one with the most talent, hence getting him into the Mercedes powered Sauber and not Schumacher. But Michael turned out a bit of all right in F1 cars didn't he?
There's bound to be others, but just off the top of my head, at this ungodly hour of the day, that'll do.
"you can never be too paranoid"