QuickBooks
www.quickbooks.com

QuickBooks feature comparison:
quickbooks.intuit.com/commerce/compare/compare_result.jhtml

Timeslips
www.timeslips.com

Timeslips feature comparison:
www.timeslips.com/products/summary/features_by_version.asp

Big Picture Communications
www.bigpictureboston.com

Mark Ostow Photography
www.ostow.com