If you've run through your DSiWare points budget and you're still looking for something to do, point your browser over to DSiCade, a site for fan-made browser games.
It's only at a beta-stage so far, so you can choose among a Simon-style memory game (pictured) a Missile Command-type game (which I couldn't get to work) and a shoutbox, should you feel like bellowing your love for the DSi into the ether.
It has a way to go before it's the level of the WiiCade, but at least it is a start.