There's finally an official site for Walt Kelly's Pogo, though there's not a lot too it as yet; they've got a biography of Kelly, a list of out-of-print Pogo books (there was an attempt, about a decade ago, to reprint the whole strip, but as often happens, it didn't get beyond the first few years), and one measly strip a week.
The high reputation of Pogo among comic-strip artists (Bill Watterson, for example, cited Pogo and Peanuts as his two favourite strips) kind of obscures the fact that it was never all that popular in its time; it gained some popularity in the mid-'50s but it wasn't the sort of strip that could sell a newspaper by itself, as Peanuts could in its prime. Also, there are some things Kelly is wrongly credited for starting, most obviously, bringing politics to the comics page. Li'l Abner was doing political content long before Kelly did, but it doesn't get a lot of credit for it now, mostly because people mistakenly think it was a right-wing strip.
Pogo is mostly known now as the strip that dared to satirize Senator McCarthy, which is kind of a reductive way to remember a strip that was largely non-political. On the other hand, it's the political stuff that holds up best; Kelly's non-political humour (as in his Sunday strips, which he usually aimed more at children) is often more cute than funny, heavily influenced by the sweet, toothless, Pluto-on-flypaper physical comedy of the Disney cartoons he used to animate on. But what makes even those strips fun to read now is the detail of the artwork; comic strips back then had more space and were printed bigger, and Kelly filled the panels with physical action, things going on in the background, interesting perspectives -- it's anything but a talking-head strip.