redearslider.com

Im thinking of getting a 60-90 gallon tank. Whats a good wattage for a tank around that size and are there any brands i you recommend or stay away from?

stealth heaters are great. Everyone loves them. Don't really know about your heater watt question.

Check out the water quality section of redearslider.com, there's great information and a formula to answer your question. I agree with daddyskittles as well, I got a stealth heater a week ago and my temps have been rock solid. I have it in the largest recommended amount of water for its wattage and during the day it stays a perfect 78, only dropping to 77 at night. My last heater was All-Glass aquarium, and I wouldn't recommend it. It worked fine for about 6 months, although not as accurate as the stealth, but it's completely shot now. The thermostat stopped working, so no matter what I set it for it heats the water to 85.

Glass heater+turtles=possible horrific disaster involving electricity and glass.
Stealth heater +turtles=no possible glass in tank. This is my reason for the stealth, and of course, it does keep the water at a more constant temp.

3-5 watts per gallon is fine. My choices in this order would be: Stealth, Ebo Jager and Tronic.

there should be a key on the back of the box that will tell you

this wattage ~ this many gallons
this wattage ~ this many gallons

and so on.

I have a 90 gallon tank (60 gallons of water in it) and I have a 250W stealth heater ("black plastic tube" that is fully submersible). It works GREAT & was worth every penny since I no longer have to worry about my big adult RES banging the heater off the side of the aquarium glass.

The water stays around 77 degrees but I can turn it up if I need to.