University of Texas at Austin
Tex's French Grammar: Regular "Ir" Verbs Present Tense
This site from Tex's French Grammar, which is provided by the University of Texas, is a wonderful site with clear explanationsof regular "ir" verbs with written and audio usage examples and interactive practice exercises.
Language Guide
Language Guide: Irregular Stem Changes
Learn and practice the correct formation of stem changing verbs in Spanish. A link to interactive verb conjugation practice is provided under the grammar explanation.
Language Guide
Language Guide: Preterite
This verb conjugation site is a great review of the formation of the forms of the regular preterite forms as well as those with spelling changes, stem-changes, and irregular forms. All sections have links to verb conjugation practice.
Study Languages
Study Spanish: Preterite Part 3
An online introduction to stem-changing verbs in the preterite tense. A quiz at the end of the lesson tests the student's mastery of these conjugations.