I dont usually say anything on this site, but I hate when people post things that are blatantly wrong. Sadly I am at work, so I cannot quote the things I am about to say, but I can later.
Balesir. First there is an entire dragon article dedicated to intelligent non-artifact items and they can be found on the charater builder.
And second, when wizards introduced the concept of item rarity at the release of essentials it was stated that rare items are story items they define characters or plots and are outside the realm of the player's advancement. They are not quite artifacts because they do not go away and they do not have there own motivations, but they are more than one or two steps better than an uncommon or common item.
Yes, I know all about the changes made with Essentials - they still make no sense as I will explain further.
" And second, when wizards introduced the concept of item rarity at the release of essentials it was stated that rare items are story items they define characters or plots and are outside the realm of the player's advancement." Which is exactly what they had previously defined artifacts as. Rare items are redundant; their inclusion makes no useful contribution. Further to this, at the same time they removed the requirement for "Daily Item Uses" - which artifacts never had in any case. Rare items and artifacts fill, according to this definition, exactly the same space, and they do so in exactly the same way, as I'll note next...
" They are not quite artifacts because they do not go away and they do not have there own motivations, but they are more than one or two steps better than an uncommon or common item." Artifacts 'go away' at the behest of the DM - but what item doesn't, in the final analysis? Artifacts do not
necessarily have motivations. Look at the "Hammer of Thunderbolts" or the "Shield of Prator" in MME. 'Concordance' is clearly not a requisite for artifacts.
In the end, I made my answer not because I contend that the rarity mess never happened - clearly it did. I made my answer as I did because I can offer no properly coherent answer with rarity included because the definitions of rarity are redundant, confused, ambiguous and nonsensical. An item's "power" defines its level, not whether it's an artifact or not - compare any 'Heroic' artifact with any level 25+ item to see that. An item that is "more powerful than others of its level" is just wrongly assigned a level. Rare items, as far as I can see, fit either into the category of "wrongly levelled" or into the category of "should be an artifact". The classification itself is totally redundant. Hence my answer was made without reference to something that makes no sense as part of the 4E system; to do otherwise would make my answer as nonsensical as the whole, muddled "rarity" guff already is.