open source ERP system

Hi,
I'm doing research on open source ERP systems with an intention to implement it in my client's company.
They produce wide range of signs.
I need good ordering, invoicing, material planning, stock control and crm modules, to name just the most important ones.

I've been googling now for a while to find some good product, but I was wondering if some of you could share their experiences on the subject.

Thanks
Peter