Following last week's killer deal on Batman: Arkham Asylum, Games for Windows on Demand continues its series of game sales with Street Fighter IV. Right now, the service is offering Capcom's fighter for 50 percent off, knocking the price down to a palatable $19.99. Or, if you prefer, Impulse is also offering it for the same price. Of course, it's worth noting that Super Street Fighter IV will be released in just a month, so you might just skip the whole thing and wait for a couple of weeks.
Unless, of course, the allure of "a nifty little special set of things" is just too much to resist.
Source - Games on Demand Spring Sale
Source - Street Fighter IV on Impulse