It would be great if this kind of thing were on LORE. I ought to gather what I can and put together a wiki page, then someone can post it to LORE.
But in the mean time, what I usually do to answer the level limit question is rely on the albums of Kat's Creations and the Freelancers.
The Freelancer'sKat's CreationsThese stores have item descriptions for most items, and the Freelancers especially have gone to great lengths to add the level requirements.
For example, +2 Stat rings require level 12.
So check out these excellent albums, and be sure to thank them by sending your business their way.