Johnny Vander Meer's record of consecutive no-hitters in 1938 might be the more popular record, but Ryan's is the more impressive.
There are an average of three no-hitters every year in baseball (five so far in 2010), but it's not often that you see many pitchers repeat the feat.
For perspective there have been 26 pitchers in the history of baseball, not including Ryan, who have ever thrown multiple no-hitters (the most recent being Mark Buerhle in 2009). Here is the list of pitchers who have done it at least three times: Larry Corcoran (1880, 1882, 1884), Cy Young (1897, 1904, 1908), Bob Feller (1940, 1946, 1951), and Sandy Koufax (1962, 1963, 1964, 1965).
Ryan did it seven times (1973—twice, 1974, 1975, 1981, 1990, 1991). In 1991 Ryan became the oldest pitcher to ever throw a no-hitter. He was 44 years old. Try beating that one, Jamie Moyer.
With hitters having access to advancing scouting reports, it's borderline impossible to see this feat ever equaled.