Strength training using 1 dumbell. Good idea?

I purchased some Powerblock Dumbells and absolutely love them! Only thing is they are quite pricey =/ My partner also wants to start working out but we can't afford to buy another set for him at the moment.

We want to just do strength training as live in a flat. Does anyone else use 1 dumbell for strength training exercises? If so does this work well? Any other suggestions welcome too :) Thanks guys x