iPhone/iPod touch: QuickCal, a smart appointment-making app that understands exactly what "Lunch at noon tomorrow at Swifty's for 45 minutes" means, is now available in the App Store. It worked wonders as an OS X widget, and definitely survives the mobile transition.
QuickCal integrates with the calendar on your device, which you can then sync to Google Calendar for greater access. On the whole, QuickCal is a much nicer way to put events into your schedule. It understands the who, what, where and when of your appointments, makes contacts and phone numbers easy to dial from the app, and shows you what it's about to enter in as you're typing out plain text. It lacks for an iPad-specific version at the moment but, man, that will likely be nice when it arrives.
QuickCal Mobile is a $1.19 download for iPhones and iPod touch models.
QuickCal Mobile [iTunes App Store]