Like Quicken:
http://kmymoney2.sourceforge.net/
http://www.gnucash.org/

Very powerful and robust, like Quickbooks:

http://www.sql-ledger.org/

See also: www.desktoplinux.com/articles/AT2282537026.html (this is
old, but I checked Codeweavers and quickbooks sort of works in Linux)

www.codeweavers.com/.../?letter=q;

Hover over the Codeweavers icons to find out what they mean.

This application is considered by many to be the single biggest drawback to
switching to enterprise Linux due to Quickbooks' prevalence in small
business and the lack of file compatibility. You can always go the
VirtualBox route.