GLTC, do have some lovely storgae soloutions, though are very expensive for what you get. keep an eye out on Ebay as there are a couple of companies that sell their surplus stock, brand new but at a fraction of the cost.
Storage cubes are good, depending on the age of children and how often adults, including other parents will be using them. I don't like bean bags for adults as they are big, always look messy and a nightmare to get in and out of!
A bench is also good, with storage below. If you have a small space, it may be worth getting a local joiner to build you a simple MDF unit that is designed to fit in not only the small stuff, but as Metatron pointed out, the larger stuff too, which in a small space can start to look messy, quickly. It can then be painted the same colour as the walls and is less intrusive and you get much more storage this way.
Ikea do some great rugs that double up as play mats, again would depend on the age of children.
I have a sofa in my playroom, but that's because I have a young child and all visitors have young children so we spend most of the time with them at the Moment. The Ikea Klippan is great at around £130 with washable and removable covers. But might be too big is space is limited.
Storage, seating and a surface for drinks etc are the key ime.
HTH.