OK, some clarification is definitely required here.
This myth of the "valiant Poles" charging tanks is a load of huey, but it is still widely reported in Western history books. The whole story is a fabricated piece of Nazi propaganda based loosely around an incident on the closing day of the Bzura River battles in September 1939 when withdrawing Polish horse cavalry found itself encircled by a Nazi light tank unit. They did what every military unit in that situation does, they fought their way out. Horses were faster and more maneuverable than tanks in 1939 so as soon as they broke out they ran, which is the sensible thing to do in that situation. They did not charge steel tanks with their lances; give us some credit. The Nazis used this incident as propaganda to illustrate how vastly superior Nazi tactics and equipment were, and how backward and hopelessly medieval (i.e., history) the Poles were. I may remind you that for as short as the Nazi invasion of Poland lasted, 35 days, it was still 5 days longer than the combined French, BEF, Dutch and Belgian forces lasted in 1940 with far greater advantages in numbers, equipment and terrain than the Poles had.
As for horse cavalry; the roads in 1940s Eastern Europe, especially as one traveled progressively eastward from Warsaw, deteriorated in quality to such an extent that tanks, trucks and heavy vehicles became useless, especially in the Spring and Autumn wet seasons. Throughout the entire war both the Nazis and Soviets maintained large horse cavalry divisions, mostly for transport and hunting partisans. Western Europe had wonderful and complex road networks that allowed motor vehicles virtual free reign in all seasons, but horses were still more effective for parts of the year in the East.
As for the last (horse) cavalry charge in history; it may still be happening. I'll bet that if you dug into the records on last year's American-led overthrow of the Taliban in Afghanistan, you will find an example of a charge by horse-bound units. I know parts of Arabia and among the more remote Berbers of North Africa horses still dominate military culture, as they still do in many parts of Afghanistan and Central Asia.