I give my vote for Sql-ledger.org
One time surf in manual and mailing-list for setup (Postgresql+Apache) and years of using it after. I can generate all the invoices and yearly reports i need with few clicks, (from where-ever since its web-based).
Only wish, it would be connected with some webshop like Zen-cart.org
Frontaccounting looks maybe similary simple, but i have not tried it.
(Also since its using mysql, interconnection with zen-cart would be thinkable i guess, but i know nothing about databases really.)