I don't always write when I have an Internet connection available. My more productive writing experiences happen when I write on my iPad with the WiFi disconnected or turned off.
But when I do write with Internet connectivity I have my Internet browser open to three sites:
1) Pandora. I write best to music and Pandora offers a plethora of songs and variety. My choice of channel changes on a regular basis, but lately the "Train" channel seems to get my creative juices flowing best.
2) Dictionary.com. This is a great website for double-checking the meaning of words or finding the right synonym for a word to avoid repetition. It's a one-stop-shopping opportunity to making sure I'm choosing the correct wording for the correct situation. I've actually been surprised a few times to come here and learn that a word does not mean what I thought it meant. Inconceivable!!
3) Google. This one is dangerous, because I think we've all had the experience where we are trying to verify the quadratic equation and before we know it we are learning about the mating habits of poodles in China. It is a wealth of information but not good for those of us with ADOS (Attention Defici--- oooo, squirrel!!).
How about you guys, what are your Internet tools of choice while writing?