My employer has a company sponsored SIMPLE IRA plan, of which I've contributed the maximum amount ($6,000) for the current tax year. I also have a Roth IRA account established in the previous year. I am single, and don't expect my annual earned income to exceed $60,000. Can I still contribute up to $2,000 to the Roth IRA for this tax year? Is there an income level after which I would not be able to contribute to the Roth IRA?

You can still contribute to the Roth. The contribution starts to phase out for single people at an income of $95K, and disappears completely at an income of $110K. The phase out range for married couples filing jointly is from $150K to $160K.