We’ve discussed the hassles of dealing with multiple timezones and distributed web-working teams before. New site World Time Engine (in open beta) tries to bring order to this chaos. At root, it’s a huge database: type in a location (like “Scotland” or “Indianapolis” and it will show you the current time – with choices if your chosen location is ambiguous. But there’s a lot more here as well.
The best feature for web workers is probably the meeting planner – type in a whole set of locations and a proposed time, and it shows you what that time, and other times, works out to across all those locations. They also have a phone interface and a developer API available. You can also purchase their timezone maps for use in your own web site.