The options are endless. For the the money it's hard to beat the acrylic cases like Carney Plastic makes http://www.carneyplastics.com/default.htm They make wall cases for 1/24 but I use their 10 car 1/18 case, they are deeper and allows more space above each model so they don't looked crammed in.
The one on the right has 1/25 models in it.
If you want them more decorative, say for the living room or den, add a wood trim frame around them like the one in the center of this photo. It's only 4 pcs of wood and slides over the case.
Keep your eyes open at yard sales for old "Insider Storm Windows". Here's a wood frame I made with one several years age for some 1/43 cars.