Web tool. It came into your work flow this year and now you couldn’t live without it. It has simplified or improved your online experience.
Skype, hands down. Not only does it make it ridiculously simple to video conference into a meeting at the Illinois office from my Virginia home, it also keeps an incredibly long record of your conversations. This comes in handy for a) remembering what tasks ought to be on your to-do list, b) catching up when a discussion happens while you're not online, and c) proving that you did, in fact, declare that rather important fact three months ago, even if certain people do not remember the conversation.