Myob. Dead easy to use and heaps of helpful online resources.
Yep this. It can be as simple as you want it or as complicated as you need it. We started using it just to record sales and expenses at home for the business. Now we've upgraded so we have a live version where DH can record his invoices out on the job, email it instantly to the customer and it syncs with the PC back home, relieving us from mountains of data entry.

I've used a custom designed program and Arrow accounts package and both had nothing on MYOB.