Do you want a specific type of ROS or just an overall ROS/RNS measure? IF the latter, a simple DCFH would do. You don't' really need a kit. The assay is pretty common but it's not terribly specific.
Like this: http://www.sigmaaldrich.com/catalog/product/sigma/d6883?lang=en®ion=US
Be aware that there are many caveats to the various fluorescent ROS indicators. For your experiment DCFH is probably best, but you really need to make sure you have good controls (positive and negative). I recommend looking at some papers by Dr. Ischiropoulos
You can use the Amplex red kit, which measures the hydrogen peroxide production, but you need to isolate the mitochondria from your cells/tissue. Otherwise, you can use probes such as CellRox (not really specific) or MitoSox (more specific to superoxide anion) and evaluate the relative fluorescence by confocal microscopy...
No, I am just looking to measure the total intracellular ROS. The review paper Peter mentioned seems to say that DCFH can't be reliably used for this. But I guess this is the best there is for doing this?