To make crafting cool, I think you should really consider each item, and make it's creation story-book unique. It can involve the need for the blood of a dragon, or it has to be made at midnight, during a thunderstorm. Or a demon summoning ritual, in which you actually arrange the candles (a'la Ultima 7/8) and if done incorrectly it could have some interesting consequences (an escaped demon storyline). a virtual amount of time has to pass ( ie the character spent a day in the ruined temple), and seeing related descriptive text can certainly add to that experience.
I, like some of the previous posters, feel ambivalent about crafting in RPGs. I really didn't like the endless junk management of TES games, and I didn't enjoy the neverwinter 2 version too. Having automatically known recipes isn't immersive or fun, and insta-crafting doesn't sound very PPG like at all. It something that fits an action mix/max game like Diablo. I think that the Witcher's alchemy is an example of crafting done right. It wasn't a must, it wasn't a chore, and the various items used were used based on "color" and quality coding, which made it both logical, and less of a bother, since you could mix and match based on what you have found. And as a bonus it had some investigative elements.
As for the items themselves, I feel that the fun items are unique. They are rare, and they feature a cool story. When too many of those appear often in a game they loose the appeal. Generic player made items are not fun, unless they were really hard to create, and are the result of a long story line (something BG2 did for example, or one of the ideas above). It's really hard to imagine a TES recipe book kind of crafting being fun.
And, speaking of TES gathering random stuff was a chore, especially since it involved a lot of inventory management. If you decide to do it this way, please make sure at least to have a separate inventory for them, with some built in sorting, and no weight limit on flowers. (grind them into powders, for realism's sake) -Great Wizard