Not Updated For Current Season
Nidalee is one of my main champs and she is really fun to play. Her cougar mode rapes a lot and her spears hurt so much in mid/late game.
Although you don't need that much mpregen, I prefer it as it gives you great sustainability + Doran's Ring. The Magic Penetration is pretty self explanatory. The Health just gives you a bit more edge when it comes to laning and that is the time when Nidalee is most dominant.
I like Doran's Ring at the beginning for the extra Mpregen and the AP, although it leaves you without pots. The Boots allows you to spam your skills a bit more often and the Sheen gives you a bit more bonus damage after you leap on them, and so you can use the Sheen's passive + your Q which does a lot of damage. Before your Sheen, you can also get a Mejais if you find it suitable and/or you think that you are dominating your lane. The Guinsoos is beneficial as Nidalee is hybrid and the AS stacks with your heal. Deathcap is pretty self explanatory. And so is the Lich Bane. Here is where it gets tricky. The Hourglass is pretty optional. Sometimes I go for Abssysal and sometimes I go for a Guardian Angel. I hardly get Hextech either. As I said before, you can go for another AP item. Sometimes, but very rarely I get another Deathcap. It depends on if you are dying a lot or not.