Not nearly as attractive as the ideas already mentioned, but we have a wood pallet leaned up against the wall that works as a bike rack. We have one of those floor mats - like retail stores have right inside the door - underneath them. Our cat would never leave alone bikes hanging up anywhere so this was the best we could get (plus it was free). It fits four bikes. We plan on moving again soon to a bigger place so this works for now. If you're going to be there for a while those towers would be nice.
2009 Surly Cross Check
2003 Cannondale Bad Boy
Motobecane Nobly (60's or 70's)