I am new to the jeep nation. After 37 years I finally purchased an 08 wrangler and after a week truly love it. I have got to get rid of those skinny factory tires and was wondering what the largest tire I could use was without any lift. Any help is appreciated.  

I've seen em with 285' a/t's not lifted looked good, I have no idea how functional they are.

I haven't even driven one yet other than the countless number of them on and off my truck across dealers parking lots  

This will partly depend upon which package you have and/or which springs you have. There are at least 24 different spring options for the JK. I have an 08 4 door X that came with 32 inch tires. By way of comparison mine has 3.73 gears, (lowest available on a non-Rubicon in 08), and factory tow hooks. I would have no problem fitting 33's.
Can't answer if you have a 2 door  

My new jeep is a 07 4 door JK. I put 255/85/16 cooper ST on it with no lift. I bought a spacer lift, but I really do not need it, so I did not install it. It works out to a 33.5 tall by 10.5 wide tire. No issues with rubbing or decresed turn radius. The jeep looks good with this tire. However a better set of shocks would be nice. It seems I sway a little more with the bigger tires. I think a good set of shocks would help. My jeep is a 07 and has the 4.10 and 6 speed. This works good with this tire height. Gas mileage sucks in stop and go and around town, but works out to 16-18mpg on a recent trip, which is what I got before with the smaller 225/75/16 tires. The 3.73 would give you better gas but less power.  

Tire width is more critical than height. You are generally safe with about 1 more inch of height(if you are starting off with 31 or 32 inch tires), but if you add say 30 mm. to width, then you will probably rub against the sway bar at full lock. I have a 07 rubicon and have the 33 in. (285x70x17) BF Goodrich KM 2 tires. Height is fine, but little rubbing at full lock in mostly right hand turn. In reverse, no rubbing. I can picture why, but Jp staff could explain much better than I. Hope this helps. Just noticed the date, 9 months later cant help much.