There is a pretty nice PID library already for the arduino.http://playground.arduino.cc/Code/PIDLibraryhttp://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/
If you don't need to measure temps over 300F, the LM34/35 monolithic temp sensors can save a lot of work. They are linear and will likely interface to the arduino with no additional hardware. http://www.ti.com/lit/an/snoa748b/snoa748b.pdf
I don't know if they meet your requirements but, if you can use them, they save a lot of work. They can even be used with cheap DMMs for a direct temp readout.
Think about what you need the arduino to do.
1. Measure temp. (trivial)
2. Control resistive based heater relative to sensor feedback. (I assume)
I once did the same with analog hardware components to control a desktop mini fridge. If I had known about arduino then, it would have been a whole lot easier.
You could probably even get by with a simple high low switching setup and get by.