Vortech kits are the most complete. The V3 with a 3.47 or a 3.33 pully will put you around at 580-630rwhp. It comes with good 67lb injectors (bigger then all kits I have seen) and a huge intercooler. Most bang for the buck kit I think. That is what I have. Now the ECS puts together some killer kits that have the potential to make killer power if you deside to push it.
The Centrifugals are very easy launch and are deceivingly fast. But they lack that kick in the pants the positive displacement have off the line. So if you're looking for just a very fun street ride I would go with a positive displacement. If you're not looking for crazy power the Edelbrock eForce has a good deal right now.
That's my 2c