I have a few pieces of furniture from IKEA that have become great with a little upgrading. I painted my Rast dressers to look like Draper chests and now I want to freshen up my Hemnes TV unit. I love the shape of the Hemnes dressers-- I've suggested them to clients even if they aren't on a budget because they're really sturdy, the drawers run smoothly, and the simple silhouette works so well with everything.
But "simple" is also a problem with IKEA stuff. I plan to jazz up my TV unit by upgrading the knobs to brass drop pulls. This is possibly the easiest upgrade ever, but it makes a huge difference. Most IKEA drawers use single-mount pulls, so these will work with a lot of different pieces.