[itsameta4]

The Republic of Ireland's constitution guarantees a member of the Dáil (Lower Parliamentary house; similar to the US House of Representatives) for every 20-30,000 people, and districts are redrawn and reapportioned frequently.

This seems to be a pretty ideal number to me - it's about the size of the township I grew up in. Many people in their district would have personal ties to their representative, as a further detriment to attempts at lobbying/corruption.

The US constitution used to have a similar provision, but this was abandoned by the ammendment process in the late 1920's.