Well this is interesting. The top searches for the major search engines have (almost) nothing common.

Google.com - Top Searches in 2006

1. bebo
2. myspace
3. world cup
4. metacafe
5. radioblog
6. wikipedia
7. video
8. rebelde
9. mininova
10. wiki

Yahoo - Top 10 Overall Searches

1. Britney Spears
2. WWE
3. Shakira
4. Jessica Simpson
5. Paris Hilton
6. American Idol
7. Beyonce Knowles
8. Chris Brown
9. Pamela Anderson
10. Lindsay Lohan 

Lycos Top 50 Search Terms for 2006

1. Poker
2. MySpace
3. RuneScape
4. Pamela Anderson
5. Paris Hilton
6. Pokemon
7. WWE
8. Golf
9. Spyware
10. Britney Spears

AOL Search Overall Search

1. Weather
2. Dictionary
3. Dogs
4. 'American Idol'
5. Maps
6. Cars
7. Games
8. Tattoo
9. Horoscopes
10. Lyrics
    

I also couldn't find a top search terms list for Ask.com, but the About Ask.com page has the top Ask.com searches for the week.