Obviously I'm not talking about ranked play or taking this seriously, but "What non-marksmen mage do you think would make the best adc? or better yet the most fun to use as an ADC.
Personally I'd say Leblanc because of all of her utility and her escape, or possibly Veigar because his ult scales off of other AP and his stun would be awesome for an AD carry.
Anomander2 votesTF or kennen
The Ruin Sage1 votesTF or kennen
kennan is already a marksmen though and I use him quite a bit for adc actually. TF is good though
The Mormonator2 votesOther than the ones already mentioned: Orianna Magic Damage on hit and controllable warding so you never lose vision.
Syn Zykan2 votesFor me it is a tossup between: Annie, you can choose when to stun and great range. And her shield on E gives her some decent defensive stats if you need it. Ryze, Manamune + Trinity = OP weaving AA's between spell casts.
The Ruin Sage1 votes[{quoted}](name=Syn Zykan,realm=NA,application-id=cIfEodbz,discussion-id=ojdckrJ9,comment-id=0002,timestamp=2015-02-06T03:47:34.590+0000)
For me it is a tossup between: Annie, you can choose when to stun and great range. And her shield on E gives her some decent defensive stats if you need it. Ryze, Manamune + Trinity = OP weaving AA's between spell casts.
is there a full build guide for this ryze? that actually sounds really fun to try
Syn Zykan2 votes
Masteries: http://prntscr.com/61mu2c
Runes: http://prntscr.com/61muld
Build tear into lucidity boots, then build into Trinity force starting with Sheen. Once tear is almost fully stacked upgrade it into manamune. I normally go for the Bloodthirster before IE and get a Last whisper when they start to get armor.
You don't really need any attack speed either, since you will be using your spells between autos, it would be wasted. I definitely do not recommend this for ranked, but it is fun if you can pull it off nonetheless XD
If you need armor: 
If you need MR: 
OR 
The Ruin Sage1 votesill definately give it a try
Raemar2 votesI remember seeing a build for Karma a while back that basically focused on abusing her passive to be able to spam her R on an obscenely short cooldown. Could be pretty fun between all the control and sustain you could get out of it.
PyroPup1 votesMachine gun Lulu can be fun.
2000boxes1 votesleblanc she has self peel a low cooldown escape her ult gives her another way to escape
combine that with strong auto attacks you have? a modified version of vayne
Vaypoure1 votesI've seen AD 
do well.
Cindikle1 votesAhri Mobility on Q Mobility on R E for CC If you build Muramana I think her W will proc it on all 3 hits. Could of been changed last year though.
Karma Passive+AS build = many many mantras. Full build your R will be up for every W cast. Giving you a 40% missing HP heal on a 10s cooldown that roots a target for 2 seconds. As well as the MS boost on her E and the slow on her Q. Her AA animation is clucky though so use in moderation.
Zilean Has 600 range, MS buff, free GA. Like Karma though, his AA animation is not great for an ADC.
Vel'Koz Great animation. Low mana cost on abilities with good CC if you can land them. Passive makes his abilities still do good damage even without AP.
Viktor I believe Q is an AA reset. Which will give you some hard hitting mixed damage as it converts 100% AD into magic damage. W will give you some strong zoning. E likely used mostly for vision in bushes. R has quite a bit of damage. One of the highest in the game if you use all of it.