MacWorld posted a quick summary of some accounting programs for Macs. I know that not everyone out there uses Apple products, but half of the article was geared towards web-based solutions as well - so I figured the post was worthwhile.

One of my favorites is QuickBooks Online. Here's what they have to say about it:
"Intuit’s online version of QuickBooks offers a lot of options, even at the free level. All versions provide you with the ability to create and send invoices, charge sales tax, track payments, print checks, and track expenses, for example. Some of the more sophisticated features, like creating estimates, time-tracking and billing by customer, and importing data from the desktop version of QuickBooks are limited to the $35 per month QuickBooks Online Plus product. It’s also accessible on smartphones including BlackBerry devices and iPhones." 

Check out the complete article here.