Originally Posted by: Dave CardwellIs there a good place to learn about classical harmony and chord sequences?[/quote]
The absolute best place is the music itself. Scores are very inexpensive nowdays from places like Dover Publications:
http://store.doverpublications.com/by-subject-music.html

Or if you are adept with a sequencer places like Classical Archives have MIDI files of all the great music from past eras:
http://www.classicalarchives.com/

Or you can search the web and turn up a ton of great sequences, too. You can also try:
http://www.musictheory.net/
http://www.tonalityguide.com/
http://www.schenkerguide.com/
[QUOTE=Dave Cardwell]
I'm looking to put some of these kinds of ideas into my music. I'm thinking more along the lines of romantic and 20th century than Bach or Mozart.

How much do you already know about theory? The Romantic era composers built upon the ideas of the previous Baroque era (Bach & Mozart) as well as the Classical era. For example, the biggest single overall concept of goal-directed harmonic motion didn't really change from Baroque to Romantic. But the Romantics put their own twist on how that motion was accomplished. The basic functions of tonal theory didn't really change: dominant-tonic relationships, voice leading.

So a good understanding of these previous eras will not only help you understand the later ones, but in many cases it is almost impossible to understand without some of that knowledge.

It can be like trying to do calculus without first learning algebra. :)