Not Updated For Current Season
Nidalee is a very good support and survivor, but she is also quiet good in 1 vs 1's, in teamfights, she is not as good because she is a focus target, in human form she can heal and reduce armor/magicresistance for her teammates. Her passive is Prowl, which gives you bonus movement speed for 2 seconds when in a bush! so you can run out of bushes but still be a little quicker. (Also in cougar form the run animation for it looks so cool!)
You wanna take Magic Penetration, because you do more damage (obviously), health per level because she is really squishy earlygame, but you can build this up. Cooldown reduction so you can spam her heal, (If you've got a dorans ring and the blue buff!).
You wanna go with a 9/0/21 build focussing mainly on cooldown reduction and magic penetration in the offense tree. Take health and mana regeneration in the utility, along with buff durations, mana regeneration, and cooldown reduction.
Start off with a Doran's ring, you will need the health and mana regeneration from it begin game. As boots take the Ionian boots, the cooldown goes well with your masteries and its very usefull for laning against an enemy who harasses alot, this way you can heal against the harassment. Try going for a lichbane, one of Nidalee's main items, because your cougar abilitie's don't cost any mana and have low cooldown, it means that you can spam them like a madman and trigger your lichbane each autoattack. A guinsoo's rageblade afterwards, the attackdamage and ability power are good because her Cougar's Q ability uses attackdamage, and the rest ability power. Your Q ability in cougar form is propably your main ability, because it does more damage the lower your target is. A rabadon's because that way your heal and other abilities do massive damage and give lots of health, afterwards get a Hextech gunblade to improve your 1 vs 1 and teamfight battles, surviving longer means more help for your teammates! In late game when you got all your items including Dorans ring, you can then sell that for a Zhonya's hourglass or Abyssal scepter, based on what kind of champ kills you the most! Ad/Ap.
Start off with your Heal on level 1, take Javelin Toss next, level between those 2 untill level 4, take your Trap then. Its usefull to take your trap before level 6 so you can jump in cougarform take your ulti on level 6, (Duh). And keep leveling E Q E Q E Q maxing your trap all the way last.
Ghost and ignite is the way to go! You don't need flash or heal, cause you got both of them, switching through Cougar and Human form to heal and jump away is so ******* annoying for the opposing team they will all ragequit. :D Ignite is for when you want to snipe someone with your Javelin toss, but aren't sure it will hit! so you can ignite then throw your Javelin toss, so its a no-escape death!
All together, Nidalee is the champion for you, if you like to heal and kick butt, or if your just a hit n run kind of person! Shes best in a solo lane, but in teamfights she may go wrong, her abilities are fun to expiriment with! But too much will make you lose the game.
Good luck and have fun!