As a Jayce player, I can say Jayce is easily one of the hardest opponents to lane against. I'm not suprised this thread popped up, since again, he is a very hard top lane opponent. So, here's what I would suggest, in laning against him, from my expierence.
First of all, the only person I've met in lane that's countered me is Yorick. I'm just tossing that out there.
Personally, when I play Jayce, I use in melee, I use my Q, then knock them back with my E for general harass. Some players may argue it's easier to use E - Q to harass, maxing your Q first, but I personally max my E first. That being said, if the Jayce your laning against is using his melee E for most of his damage outputs, you would want to have some magic resist in your build. Even if the enemy team is all Physical. What a lot of people don't know about Jayce is his E does 20% of your heath (I believe, not sure on the stats) as magic damage, and some physical damage. So again, if the Jayce you're laning against uses E a lot, magic resist.
Also, I'm sure someone already said this, but once your Jayce goes into Ranged, his kit becomes a lot less versatile. Use that frame of time while he's in ranged to get some good damage, and back off, because the minute he switches to melee, you're going to be E'd to doom.
To conclude, for the most part Jayce will push your lane and you will be tower hugging a lot. So, ganks from your jungler are going to be extremely helpful. Especially if you're jungler has tons of CC, because if you're jungler is Warwick, and you're laning as, let's say, Fiora, by the time you guys do your damage, if the Jayce is tanky enough, he'll just use his speed buffs to run away, probably not even burning flash. So ganks are essential.
If you were too lazy to read that, here's the extremely short version of it:
-Melee E is dangerous, and it does magic and physical. Keep that in mind.
-Try to do your main damage output while he's in ranged mode.
-GANKS! Get that super Seljuani CC and gank him all game! SHUT HIM DOWN!
-Yorick is a pretty decent counter against him. (From expierence.)