Tides

Online Tide Predictors
UK
UK Hydrographic Office Tide Predictor
The United Kingdom Hydrographic Office operates a web-based Tidal Prediction Service, called EasyTide.  EasyTide allows you to obtain a 6 day forecast of the tides for selected ports

PBO on-line tide predictor
On-line tide prediction service for 23 major U.K. Ports provided by PBO. 

World
Tide and Current Predictor
Uses Census Bureau's TIGER mapping technology to generate tide and current predictions for most of US and Canada and some European and Asian locations.

USA
Saltwatertides.com
Tide, moon, and sun predictions for the Gulf Coast, US East Coast and US West Coast

Harbortides (US)
Tide information for US and Hawaii locations

Computer-based tide predictors

There are a number of software programs that offer the user the ability to predict tides.  No endorsement of these products or any other product is implied.  You are strongly urged to form your own opinions regarding the suitability of these products for your own use.

Belfield Software Tide Plotter 2002
At only £9.95 for a Windows and Windows CE package this is a great little program.  It covers the U.K. and some ports in Ireland, Holland and France.  The only drawback is you have to buy a new version each year.  It does however save you carrying an almanac around with you, particularly useful if you have an Compaq iPAQ or any other Windows CE device.

AutoTide Prediction program
Produced by Linden Software, this program is available for free download off the web and then you can purchase a licence key to enable future predictions.    There are three flavours of the product, Voyager, Gold and Publisher, with prices ranging from US$ 49.99 to US$ 99.99 (between about £35 and £70 depending on exchange rate fluctuations).