'obama'
Most frequent examples: 
[obama, michelle obama, obama s, barack obama, obama speech, obama press conference, obama press, obama acceptance speech, obama acceptance, obama inauguration]

'american idol' 
Most frequent examples: 
[american idol, american idol results, american idol top, american idol april, american idol may, american idol march, american idol results may, american idol winner, won american idol, who won american idol, american idol final, on american idol, voted off american idol, american idol bikini, american idol season]

'day' 
Most frequent examples: 
[day, s day, fathers day, day of, mothers day, day parade, day 2009, day comments, earth day, day cards]

'earthquake'
Most frequent examples: 
[earthquake, usgs earthquake, diego earthquake, san diego earthquake, california earthquake, alaska earthquake, earthquake california, earthquake san, earthquake map, earthquake news, earthquake in, bay area earthquake, earthquake los, los angeles earthquake, earthquake information]