Just adding a couple:

Wenn hinter Fliegen Fliegen fliegen, fliegen Fliegen Fliegen nach - When flies are flying behind flies, flies fly behind flies.... sounds better in German.

Also, a similar one:

Wenn hinter Griechen Griechen kriechen, kriechen Griechen Griechen nach - When Greeks crawl behind Greeks, then Greeks are crawling behind Greeks. Again, doesn't translate very well.

Source: my childhood memories