BMW offers a pannier system for the F650GS. The special quality of these panniers: They are extensable to 31 l each. The picture shows the "compressed" state.
Your local BMW dealer
Well reputated German provider Touratech offers pannier system for F650GS/Dakar in two sizes: 35 l each and 41 l each. The whole system consists of two aluminium panniers and a tube type carrier for mounting on the stock mounting points.
Price: DEM 1049.- (EUR 536,35) each (premounted DEM 1149.- (EUR 587.47) each)
Five Stars offers a carrier for GIVI panniers.
Price: DEM 219.- (EUR 111.97)