PRGPRODUCTS.COM
Best leveling kit available. Awesome guy to deal with. Extremely knowledgeable about Titan's specifically. Great customer service.
There are no Titan's available with a factory installed leveling kit. As someone noted earlier, the ones that go ontop the spring are a huge problem. They will destroy the shock.
The majority of the spacers that install ontop of the coilover itself are fine. I still recommend the PRG version though. Note that there are different versions for 2wd and 4wd trucks.
You can't go wrong with a leveling kit, won't affect your ride at all. You may have to get an alignment afterwards.
Try out Titantalk.com or clubtitan.org for a plethora of information.