I have about 8 or 9 of these
across the back wall of my bike storage facility - they are from Roseversand (Euro 7.30 each .... and the postage from Rose is now only a flat Euro 5.95 for any order*)
They are excellent ... the channel keeps the wheel aligned and the hook has a heavy-duty rubber cover to prevent damage to the rim
Tortec also makes the same type - but they are a lot more expensive (about £13 I think)
Rob
* even with the poor Euro rate the stuff from Rose is pretty good value - and it usually arrives within 3 days.