Shure GLXD14R+

The system is rather expensive but you'll get your money's worth. I use this wireless system for bass guitar and it is one of the very few systems that actually delivers without choking or cutting off low-end.
The belt-pack is made of sturdy aluminium with no unnecessary bells & whistles and a rechargeable battery.
The receiver-unit is rack-mountable and contains a charging slot for an extra battery, which is brilliant. As well as a charge indicator in battery time remaining instead of a percentage.
The system is very easy to setup and use, and the included rack-mount kit is a bonus.

The only flaw in the system is the cheap Jack-connector on the transmitter cable with a Shure sticker on it. This connector causes intermittent connection failures when inserted in my instrument.
If I use a cable with proper Neutrik Jacks instead with my instrument, there is no problem at all.
It is a pity that Shure charges 45,- Euro for that little cable and doesn't have the decency to outfit it with a proper quality Jack-connector (preferably Neutrik).
Other than this little flaw, the system is perfect and I can highly recommend it for bass players.