A number of major economic upheavals have received proper-name billing. Thus, for example, Wikipedia has entries for or allusions to the "South Sea Bubble," the "Panic of 1819," the "Panic of 1837," "Railway Mania," the "Panic of 1857," the "Wall Street Crash of 1929," the "Great Depression," the "Great Recession," etc.
This does not resolve into a consistent, predictable pattern, however. For example some sources refer to the "Mississippi Bubble" and others to the "Mississippi bubble." Likewise, some sources give "Tulip Mania" and others "Tulip mania". And some economic upheavals—such as the "dot-com bubble"—have tended to remain lowercase despite being widely identified by that particular name.
In the case of the global financial crisis of 2008, the predominant form thus far seems to be lowercase, but this may be due in part to common variant forms such as the "2008 global financial crisis," which, like "1857 panic" and "1929 stock market crash," lends itself to a lowercase treatment because it uses financial crisis generically, with the year as the distinguishing modifier.
In the fullness of time, the "Global Financial Crisis of 2008" may take its place among the widely acknowledged proper-named economic disasters of Western history—but so far, people have been far less willing to treat it as a proper name than they have (for example) the "Great Recession" that followed on its heels. And until support for treating the common name as a proper name becomes significantly firmer, you are likely to see the "global financial crisis of 1989" remain the more common treatment of the term.