Verb Conjugator http://users.ipfw.edu/jehle/VERBLIST.HTM This link is a great reference if you need to check the conjugation of a verb. The list of verbs is quite comprehensive and if you can't find the verb you're looking for, see if you can find a similar one or one with a similar root.
Diccionario Español/Inglés http://www.diccionarios.com/ A useful dictionary for Spanish. It also has French and Catalán (Barcelona region).
Spanish Listening Practice http://www.laits.utexas.edu/spe/siteindex.php This site from the University of Texas, Austin is great for practicing listening comprehension. There are different levels from beginning to advanced and there are videos as well.
AP Directed Response Questions http://www.learnalanguage.org/apspanish/ A great site for AP students who want to practice the 5-question directed response portion of the AP exam.
Extensive Spanish culture and language http://cvc.cervantes.es/portada.htm An amazing website for learning everything there is to know about Spain. There is also an excellent section called "Aula de lengua" for Spanish language lessons (check out "Pasatiempos de Rayuela").
Univision online http://www.univision.com/portal.jhtml Here is a very diverse website to find articles that will fit every interest. Take some time to check it out.
Great Spanish Music Lyrics and Music http://lacuerda.net/ This is a great site if you want to find the lyrics to a song in Spanish or if you want the chords/music to a song in Spanish.
Great Spanish Music online http://www.batanga.com/es/ Do you want to listen to Spanish music while you're working online? This site has a great variety to suit your tastes.
Idiomatic expressions in Spanish http://www.studyspanish.com/idiom.htm Want to add some more "modismos" to your vocabulary? This site gives you random ones to learn at the click of your mouse.
Podcasts about Spain http://www.notesinspanish.com/ Listen to real audio conversations in Spanish. Marina, a native Spaniard, and Ben, her British boyfriend, talk about life in Madrid.
Spanish language skill builder http://www.studyspanish.com/ This site has some good (free) exercises to practice Spanish and some more that you can pay for and assess yourself.
Spanish practice and Crossword puzzles http://www.goethe-verlag.com/tests/ES/ES.HTM A great site to practice your Spanish from basic to advanced. You can also improve your vocab by trying one of the crossword puzzles.
Subjunctive in Adverbial Clause (siempre vs a veces) http://doncarlos123.tripod.com/subjinadverbclauses.html Here is a good, detailed explanation of the use of the subjunctive with adverbial clauses. There are exercises at the link at the bottom of the lesson.