Ikea has inexpensive pillows, e.g.:
http://www.ikea.com/us/en/catalog/products/40281277/
http://www.ikea.com/us/en/catalog/products/30284323/

CB2 has contemporary and not too expensive furniture, e.g.:
http://www.cb2.com/neptune-tables-set-of-two/s642992

Something that’s not too busy for a rug, e.g.:
http://www.westelm.com/products/honeycomb-textured-wool-rug-special-order-t989/?pkey=crugs-flooring&cm_src=rugs-flooring||NoFacet-_-NoFacet-_--_-

This is what Pinterest is for. In the search box, type in "living room gray couch." Also try "living room gray magenta." I just did it and saw lots things that might work with that painting.

Bumping this.

http://www.minted.com/product/wall-art-prints/MIN-1G4-GNA/luminous

I love the feel and colors (scarlet). We're moving into new apt and I'd love to use this as a starting point. I'm going for fun, pops of color, comfortable yet stylish, sort of contemporary/eclectic, and affordable. I only have a light gray neutral sofa and need everything else. What rug, throw pillows, window covers, other art/prints, coffee table, accent chairs would you do? I need ideas for pulling it all together. Thanks!