If you're a complete beginner, you may find it useful to start with an introduction to the pronunciation of Portuguese. It's not very easy to find a good one though. Learning Portuguese has a very clear explanation of the sounds of European Portuguese, but sadly no audio. Look at it and then go to Portuguese language On-line to hear the sounds individually (click on Pronunciation) and in words (click on the green arrow at the bottom of the page).
There aren't many really good Portuguese sites on the net, and in particular very few which have adequate exercises. The BBC's Quick Fix and Talk Portuguese give a basic introduction to Portuguese for travel, covering both the European and Brazilian varieties, but there's not much practice. Talk Portuguese provides a slideshow with language and explanations, and then some video clips. Make the most of what's there by using the dialogues to create the sort of activities which were recommended in the Learning Tips article, Two steps forward and one step back.
In addition, if you're in Britain, you can also use the TV programmes which accompany the course. You'll find the schedule on the BBC site, or check in our Language Learning News section.
Sonia Celegatti Althoff 's site focuses on Brazilian Portuguese and gives a pronunciation guide, grammar explanations, exercises and more. Off putting layout but again, one of the best of a sadly bad bunch.
As you get to the post beginner stage, you can start to test your knowledge of Portuguese verb forms at Verbs On-Line.
At higher levels check out the different regional accents of both European and Brazilian Portuguese at Learning Portuguese or try reading and listening to the news on BBCBrasil.com
And if you're a teacher or home-schooling parent looking for tips on methodology, lesson plans and practical activities to use in the classroom, go to our section for Teachers and Parents.