TopicCrunch lets you choose which of the three engines are to be included in the search.

TopicCrunch lets you choose how deep you want to dig, down to the engine maximum of 1,000 hits (Google and Yahoo!). Often, using the default of 100 hits per engine is plenty.

It allows you to select a suitable sleep time between searches so that the search engines do not ban your IP address for a time-out period. More about that below.