Please check Microsoft PinPoint. You will get a lot of addon's there.
I have used only once this addon
QuickBook for CRM Online. And works perfect for me.
The main features of this product is
- Invoice Creation: create QuickBooks invoice from CRM invoice - Customer Link DB: create and update QuickBooks customer details in CRM Accounting Customer entity - Check Payment: update CRM invoice with the updated amount paid by customer and allocated to the invoice. - Import Products: Create and update CRM products, stock levels and back orders