I invented lots of skill boosting items in 3E, both as a PC and as a DM. These were far more fun to introduce than simple guirdles of strength.
My cleric gave her cavalier friend a Saddle of Safe Riding (+10), and was considering crafting some pants of surefootedness (+10 balance), but she found some Wings of Flying instead
I guess the hardest part is determining the prerequisite spell.
As a DM I gave a player the "Golden Crown of Far Shot", a rather large crown made of golden arrows. I didn't bother calculating the cost, since it is a unique item (and it is pure GOLD).
Golden Crown of Far Shot: When worn, gives Far Shot Feat even if prerequisites are not met. Also : +2 Spot, -2 Hide (it seems to reflect light even in darkness!).
What was funny was that it was the wild elven barbarian who found it (he wears leafs and branches as clothing, and everyday paints is face in mud).