I can highly recommend Design Mark Studio. His work is of extremely high quality, and he works at a great pace.
His turnaround time & communication levels are significantly better than other designers I've worked with in the past, and he has a modern approach to design. There are many designers out there and 90%+ of them produce very average work, however this is not the case when using DMS.
The designs created are being used in production in our complete product. and we're very happy.