Latin I - III. This site has vocabulary flash cards, games (memory, hangman), and additional exercises/practice for each chapter of the textbook. Just click on the appropriate textbook (I, II, or III) and then the chapter you want to study! Enjoy!
Dickinson College Caesar - text, notes, vocabulary, mp3 audio recordings
Latin IV. This is an amazing site! Be sure you notice the tabs on the right-hand side: there's a "vocabulary" tab with all but the simplest words defined for you (though you already have this in your Steadman text) and -- most importantly -- there's a "media" tab with mp3s of the entire text read in a good, classical pronunciation. I'm going to hold everyone's finger to the fire in regards to being able to read the text aloud well!
Latin IV. If you just want a page with all of the Caesar mp3s (rather than with the the text, vocabulary, etc, since you have all of that with Steadman already), here's it is. Just put the relevant chapters on you iPod and listen as you do your homework!
Perseus Word Tool (Electronic Dictionary / form analysis
This will help so much with your translation assignments that it will almost feel like cheating! It takes any inflected form of a Latin word, analyzes it (e.g., tells you the case, gender and number of nouns), and gives you the dictionary definition. Much faster (and a lot more information!) than a dictionary!