Some addictive online Spanish practice - compete with your friends @ http://www.duolingo.com/
This site has some great listening and vocabulary activities: http://www.ver-taal.com/index.htm
Learn Spanish grammar online with explanations and quizzes: http://studyspanish.com/
Online Spanish/English dictionary: http://www.spanishdict.com/
This BBC site helps you learn Spanish with an interactive soap opera: http://www.bbc.co.uk/languages/spanish/mividaloca/
Don't understand something in Spanish? This program lets you slow the playback of anything you wish to listen to. Check out the following to download Express Scribe: http://www.nch.com.au/scribe/
Conjugate any verb your heart could desire: http://turingmachine.org/compjugador/
BSP Un disfraz nuevo assignment: http://www.textivate.com/sequence-g2yjn1
Some imperfect and preterite practice:
http://www.studyspanish.com/lessons/pretimp1.htm
This has a good explanation of the imperfect and preterite, although the quiz isn't that good.
http://www.colby.edu/~bknelson/SLC/pret_imp.php
Some great imperfect/preterite practice while reading stories.
http://www.123teachme.com/learn_spanish/preterite_vs_imperfect
This has a collection of different quizzes, etc. Look under “Preterite vs Imperfect” or “Review with exercises.”
