Bonjourdefrance.com: French grammar rules followed by a short quiz to test your understanding of grammar and your French comprehension skills. Relative pronouns ( qui / que / qu' ). 10 multiple choice questions.
Didieraccord.com: French grammar exercises to improve French vocabulary and learn grammar rules. On the theme of communication. Includes exercises on French vocabulary, present participles, and relative pronouns. With audio-files.
LaDictee.fr: Site offering free audio dictation files, for different levels. Offers links to various online exercises about sentences, pronouns and grammar.
Orthogram.com: Downloadable tables of all the pronouns in French. Personal pronouns, possessive pronouns, demonstrative pronouns, relative pronouns, interrogative pronouns and indefinite pronouns.