Karen Berlin Ishii, One-to-One Test Prep for the SAT and ACT - in NYC and via Skype
I agree with Michael that if you can present strong SAT Subject Test scores to the colleges, you should. I disagree with him, however, about the dangers of submitting "extra materials." SAT Subject Test scores are NOT extra materials! They actually are part of the Common App: you just list them along with your SAT or ACT scores. "Extra materials" that some colleges ask students not to submit would include such things as art portfolios, performance videos, cupcakes (to sweeten the application perhaps?), research or science fair projects, etc. In other words, don't send extra tangible items. Your SAT Subject Test scores will be included by the College Board in their score report for you if you send any SAT scores to the schools, so unless you use Score Choice to suppress those scores – which you may do if those scores are not impressive enough to submit – the colleges will receive those scores anyway.
And what is a good score on the SAT Subject Tests? As a very basic rule of thumb, anything 600 or higher is respectable and is worthy of submission. Lower scores would be better suppressed, as they don't show mastery of a subject, and in fact, show the opposite.