Panther added a bunch of nifty things to the Services menu (accessible under the application name menu), but the coolest one is definitely "Summarize", unless you are one of those people who love to make their Macs read stuff. (You know who you are.) Select a few paragraphs of text, then go to Services->Summarize. It will open it up in a new program, with a slider ranging from 100% (the whole selection) to 0 (the single most important sentence in your selection.) Whether it's accurate or not is debatable, but it's definitely fun.
Also, if you want to talk to someone and you aren't a very fast typer (hello, madre!), and you both have iChat AV, but the other person doesn't have a microphone (we don't all have laptops, you know), you can invite them to a One-way Audio chat. The little telephone icon only shows up next to people who have microphones, so you have to go to
Audio->Invite to One-Way Audio Chat
Use it to startle your parents!