Besides standard long range AP Mages and Assassins (regardless AP or AD), lately we see some AD Carries being played in the middle lane, not as experimental picks, but yet with great success. I will go through three most played AD Carries is the middle lane in Solo Queue, but can also be seen on the professional stage.

1. Ezreal

Ezreal is AD Carry that rely on hitting his skillshots. He is also affected of the Trinity Force power spike, of course it is not necessary to play him with that item. One of the biggest advantages that Ezreal has, is the long range on his skillshots, specially his Q: Mystic Shot. Ezreal's Q is his main damage tool, whether used for poking or farming. It's long range gives Ezreal safety in the middle lane, as he can farm being out of the range of a possible gank. Adding the fact that middle lane is the shortest lane in the game, multiplies the benefit of having that long range skillshot.

Art credit: http://orekigenya.deviantart.com/art/EZreal-501560166

Another advantage that Ezreal has, is that he has escape tool, his E: Arcane Shift. Placing wards in both top and bottom side bush can almost guarantee that you are going to be safe until you get two or three core items. The poke he provides is his biggest advantage, from the start of the game until the very end. Another thing that just a little number of champions have, including Ezreal, is his global range R: Trueshot Barrage, which allow you to help your teammates across the whole map, even maybe to steal enemy buff, or an objective (ex. Dragon, Baron Nashor). Ezreal owns a lot of potential to be a hypercarry, if you use his power correctly.

However, as the game goes further, there are few traps that you can fall into as Ezreal player. The first one is using your E offensively. By this I do not mean that you should save E only for defensive matters, but you need to be sure that your team have your back, and you do not get caught without your escape tool. Also, another thing that you should be really wary of, are Assassins with high burst (ex. Zed). Be sure to stay behind you frontline, and you should not have much problems carrying games.

2. Corki

Just like Ezreal, another AD Carry highly affected by the Trinity Force power spike is Corki. Even though his spell range is shorter than Ezreal's, he still has a perfect kit for farming, as well as escape tool, his W: Valkyire. Even if forced to hug his turret, his Q: Phosphorus Bomb and E: Gatling Gun still allow him to not fall behind in CS. Those things slitghly start to change, as soon as Corki gets level six and get his R: Missile Barrage. After getting level six, Corki becomes strong lane bully.

Art credit: http://iamsointense.deviantart.com/art/League-Of-Legends-Corki-Wallpaper-335021492

What makes him so strong is the long range of his R, as well as the low manacost on it, only 20 mana for missile. Although the manacost is that low, you cannot afford yourself to just walk around and shoot missiles, because of the fact that you can have maximum of seven missiles, reloading one every ten seconds. As a Corki player, you should consider that every third missile is a Big One, dealing 50% extra damage.

Similar to Ezreal, it is not preferable to use W offensively because of the chances to get caught by the enemy team with your escape tool on cooldown. Try to poke the enemy team with your R as much as possible before you and your team decide to engage. As Missile Barrage deals damage to enemies in area, good poke before the start of a teamfight can give you significant advantage in that teamfight.

3. Varus

We are used to Varus being played as AD Carry in the bottom, but lately he is also played in the middle lane with cooldown reduction/armor penetration item build. Like Ezreal and Corki, he also has a long range skill, his Q: Piercing Arrow. Combined with his E: Hail of Arrows, he can clear entire minion wave (not on level two of course). What makes him different from Ezreal and Corki, is that he does not have any escape tool (except Flash), so he is more viable to ganks. That means that you should play more carefully and ward more than usual so you do not get ganked.

Art credit: http://limsh.deviantart.com/art/Varus-Fanart-427543629

On the other hand, Varus has really good teamfighting potential because of his skill set, the area of effect slow from his E and of course, his R: Chain of Corruption. It immobilizes the first enemy Champion it hits, and then spreads towards the uninfected enemy Champions, immobilizing them if the chain reach them. Chain of Corruption can be both a great engage and disengage tool, and that is one reason why we see him played a lot lately.

Conclusion

As you can read throughout this article, the main advantage of all these Champion is their long range poke abilities. Also, it is pretty hard to play against them because even though they are AD champions a lot of their damage output comes as Magic Damage (specially Ezreal and Corki). These champions can be played in all team compositions, but bringing them in Poke/Siege team composition allows them to show their full potential.