Singular and plural
http://es.talkenglish.com/Grammar/singular-plural-nouns.aspx
http://www.agendaweb.org/grammar/plural-singular-exercises.html
Verb to be
http://www.aprenderinglesfacil.es/2008/03/verbo-to-be-ser-o-estar.html
http://www.eclecticenglish.com/grammar/PresentSimpleToBe1A.html
http://www.englisch-hilfen.de/en/exercises/tenses/be3.htm
http://www.agendaweb.org/verbs/to-be-exercises.html
Common objects
Loads of exercises here
http://learnenglish.britishcouncil.org/en/grammar-and-vocabulary
http://www.isabelperez.com/grammar.htm
Vocabulary and grammar games
http://learnenglish.britishcouncil.org/en/grammar-and-vocabulary
Hangman:
http://www.manythings.org/hmf/
Vocabulary: recycling
Vocabulary: food
Practise your vocabulary here:
http://www.myenglishpages.com/site_php_files/vocabulary-exercise-food.php
http://www.agendaweb.org/vocabulary/food-exercises.html
Lyrics training
Countries - online exercises
Countries
New English File Beginner
Days of the week
Ai Weiwei sunflower seeds
Interesting websites for learners of English
All skills: http://www.englishclub.com/learn-english.htm
All skills: http://es.talkenglish.com/
News in 3 levels: http://www.newsinlevels.com/
Vocabulary, listening: http://drewseslfluencylessons.com/
All skills: http://www.saberingles.com.ar/
Listening tasks, videos, grammar, vocabulary: http://learnenglish.britishcouncil.org/en/
Read the news in English, links to online newspapers: http://www.thebigproject.co.uk/news/
Weather forecast
Listening tasks - links
Listening tasks with exercises: http://www.ditc.net.au/listening.asp
Listenings with tapescripts: news, songs, audiobooks... http://esl-bits.net/
Listenings with dictation exercises: http://www.nobuna.com/lessons
Listen and read along: http://www.manythings.org/listen
One-minute listenings with exercises: http://listenaminute.com
Listen and read : http://learningenglish.voanews.com/
Listening exercises, videos, songs: http://www.esolcourses.com/content/topicsmenu/listening.html
Listenings and videos with exercises and transcripts: http://elllo.org/
Listening quizzes: http://www.esl-lab.com/
Video quizzes: http://www.eslvideo.com/index.php
Listen to the radio: http://www.mediatico.com/es/radio/europe/uk/
Wath Sky News, watch live or click on 3-minute catch up: http://news.sky.com
Unreal past
http://random-idea-english.blogspot.com.es/2012/01/unreal-past.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=4567
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-91125.php
Should have + past participle
Present perfect
http://www.ego4u.com/en/cram-up/grammar/prepersim-preperpro
http://www.ego4u.com/en/cram-up/grammar/simpas-preper