I've got four of these mounted to my garage wall to hold up my bikes. The downside is you need a size specific to the tyre widtth and the mounting location is specific to the bike's wheelbase length, the upside is they're small and cheap. They're designed to clamp/hug (i.e. clug) your front tyre whilst the rear tyre rests on the ground.
99 Bikes has five different sizes and three different colours.
If in doubt, go for one size smaller, it might be slightly harder to push the front wheel in, but it will be more secure.