I agree with STX4Runner, your best bet is to start looking through the different build threads and sticky posts and start getting a sense for what you like and what you don't.
I just went through this exercise and might have some guidance that might help you know where to start.
First, nomenclature. Wheels = Rims and Tires = Rubber.
Are you looking to replace your wheels for aesthetics or some other reason?
Decide whether you want to use your existing wheels and replace only the rubber or replace both the wheels and rubber. With the Sr5 having the smaller 17" (I think) wheels you have many options.
If you're thinking of replacing your wheels and you're on a budget also consider plastidipping them or repainting them. I personally like the wheel style of the SR5 wheels but am not a fan of the silver. Check out J-BlickPhoto's thread to see what an improvement a little plastidip makes on a stock wheel.
Next, take into account what kind of driving you are going to be doing most of the time and choose the most appropriate tire to fit that need.
Not knowing anything about what you're looking for this may or may not help but after a bunch of research below is my short-list for wheels and tires. I won't tell you what I finally decided on though.
Wheel Short List:
FN Wheels, few different options
Robby Gordon simulated beadlock
Axis Regulator
Weds Adventur 18 inch
XD Enduro
Tire Short List:
Goodyear Duratrac
BFG TA/KO2