Is it illegal to video tape police officers?

Generally speaking, no.

It is currently only illegal in Illinois. The ACLU is in the process of appealing a decision of the Illinois courts to the Seventh Circuit Court of appeals. They are expected to rule in early 2012. A similar case was brought before the first circuit court recently and they ruled that American citizens DO have the right to video tape police officers under the First Amendment.

It should also be noted that it is currently entirely legal in illinois to video tape police officers as long as there is no audio involved. Only audibly recording police officers is illegal currently in illinois.