WebCalTides is a free service that provides tides, currents and sunrise/sunset calendars for your favorite tide stations. Data is pulled from NOAA (US/etc) and DFO-CHS (Canada). Just search for a station, then click the webcal link to subscribe. Works on Apple iCal & Google Calendar; maybe Outlook too.
Written by Jordan Ritter, with contributions from Paul Schellenberg to support Canadian stations. Project source at GitHub.
Update: I'd like to add more international/non-US stations, and I've amassed quite a few old harmonics files (before they were privatized), but I haven't quite figured out how to wire them up to XTide on Linux. Drop me a note if you know how, then I can incorporate many of the international stations..
This product has been produced by or for WebCalTides Service and includes data and services provided by the Canadian Hydrographic Service of the Department of Fisheries and Oceans. The incorporation of data sourced from the Canadian Hydrographic Service of the Department of Fisheries and Oceans within this product does NOT constitute an endorsement by the Canadian Hydrographic Service or the Department of Fisheries and Oceans of this product.