TTD Patch is a great tool that no TTD fan can do without. It allows better transport network, fixes many bugs and allows TTD to be played on Windows XP. Many of its uses are explained throughout this site.
This site contains helpful tips for playing Transport Tycoon (Deluxe). With a great emphasis on rail design, this site will help you turn your small, simple company into a huge, complex, efficient empire.
This site has almost all the information about TT you'll ever need. I've spent many o' hour scrolling through its endless pages of info. Suits everyone from the expert to the first-timer.
The site present 'traditional' strategies in a new, well structured way, and some enhanced methods that should enable you to make your transport company even more profitable.
Home of the TT Saved Game Manager, this site has handy bits and pieces such as a complete list of the vehicles, the music from the game, forums and more.
An older site that hasn't been updated in a while, but most of the content is still relevant and helpful. Try 'A railway building guide' and 'TTD and rail vehicles'