And while we're on the topic of fourthcore and rare items, the preeminent fourthcore blog Save Versus Death recently released a magic item PDF with some fantastic examples: the Fourthcore Armory.As a point of order because I take pride in it, it's worth noting that "Fourthcore" as a term in the 4e community typically means something other than "pre-essentials", and it refers to the initiative to create scenarios that are challenging to the player, and not just the PC.
Another good place to look if you want to make the item rarity system work is the Square Fireballs blog, which recently undertook a rebuild of the magic item list from nothing.