The people who make the cool Web-based meta-IM service Meebo (it's like Trillian but runs in a browser) have released MeeboMe, a chat widget you can embed on your Web site. [See the News.com story.] It allows visitors to see your online state (if you're using Meebo) and chat with you in real time. Here's a live demo:
You can also use it to monitor visitors to your page--everybody who has the widget showing will appear on your Meebo buddy list as a guest to your site.
MeeboMe wins the award for making the easiest-to-use chat plug-in (you need to embed only one line of code in your site), but Meebo's product isn't the only one. Stickam, for example, has a chat gizmo, and it also does video. And there are several products designed for commerce sites that let you add a "talk to me now" button. MeeboMe is also not a chat room. Users you're chatting with can't see each other, just you.
If you want to get in close touch with visitors to your site, blog, or page on eBay, MySpace, or any other service, it's certainly worth experimenting with.