"Here, Sweetlips!" -- Presidential pets B. O. (Before Obama)
NOTE: Before reading this article, you may enjoy watching AARP TV's three-minute YouTube video, "Presidential Pets" at http://www.youtube.com/watch?v=0d2GvRoEmXA .
Speculation about the Obama family's choice for allergenic-free First Dog has gone on for weeks now. Who will follow Bush's Barney into the White Dog House?
About 38 out of 43  U.S. presidents have had pets during their terms. James Polk, Franklin Pierce and Chester A. Arthur were outstanding in their presidential petlessness. 
George W. Bush's Barney recently snapped at a reporter, possibly from stress at his Lame Dog status. Bill Clinton's dog Buddy and cat Socks had gone through the transition before him.
George Washington (in office from 1789 to 1797, but a Mount Vernon, rather than a White House, resident) owned no less than 38 dogs and a green parrot. The hounds answered to names like Forester, Madame Moose, Taster, Tipler, Vulcan, Searcher and Sweetlips.  As general, Washington had generously returned British General William Howe's captured dog under a flag of truce. 
Cleopatra, favorite horse of second president John Adams (1797-1801) was the first pet romp on the White House grounds. Next came Thomas Jefferson's (1801-1809) caged grizzly bears, gifts of Lewis and Clark. When the British burned the White Housein 1814, Dolley Madison fled with three treasures: The Declaration of Independence, a portrait of George Washington and her pet parrot. 
The sixth president, John Quincy Adams (1825-1829) kept an alligator in the East Wing bathtub and liked to cultivate silkworms. Andrew Jackson, his successor from 1829-1837, filled the White House stables with racing fillies. Martin VanBuren (1837-1841) lost two tiger cubs to the zoo when Congress claimed that the Sultan of Oman had really intended them as a gift to the entire nation. Bachelor president James Buchanan (1857-1861) gladly endowed the zoo with elephants from the King of Siam, but kept two eagles from another donor.
Abraham Lincoln (1861-1865) wept when his sons' ponies died in a stable fire. A policeman who failed to recognize Ulysses S. Grant (1869-1877) fined the president for racing one of his steeds through the streets of the capital. Grant also owned some dogs, two gamecocks and a parrot.
When Theodore Roosevelt (1901-1909) brought a half dozen children with him to Washington, the Pennsylvania Avenue menagerie held a small bear, a lizard, snakes, guinea pigs, a badger, a macaw, a hen and a one-legged rooster, a horse and ponies, a barn owl and a rabbit -- plus Pete, the bull terrier, who once ripped the trousers of a French diplomat. T.R.'s conservationist efforts gained him millions upon millions of other pets in newly-established national parks and bird sanctuaries.
No cows have grazed on the White House lawn since William Howard Taft (1909-1913) kept one to supply fresh milk. Woodrow Wilson (1913-1921) put sheep out to trim the grass during World War I, when soldiers had more urgent duties. Herbert Hoover (1929-1933) adopted an opossum that had strayed onto the grounds.
"These Republican leaders have not been content with attacks on me, my wife, or on my sons," said Franklin Delano Roosevelt in a 1944 campaign speech. "No, not content with that, they now include my litte dog, Fala." Among FDRs other dogs (Blaze, Dutchess, Major and Meg), Fala the Scottie was his hands-down favorite: statues of master and dog sit together at Roosevelt's memorial in Washington.
Though Harry Truman (1945-1953) once said, "If you want a friend in Washington, get a dog," he gave away all the animals that came to the White House. One of Dwight D. Eisenhower's (1954-1961) two dogs were so boisterous that she was sent back to the family farm at Gettysburg, Pennsylvania. First Lady Jacqueline Kennedy (1961-1963) set up a play area for Caroline and John-John's dogs, guinea pigs, lambs and ponies (Macaroni the Pony would pull the children in a sleigh at Christmas. Soviet Premier Nikita Krushchev gave young Caroline her pet, Pushinka, daughter of the first dog in outer space (Strelka). Lyndon Johnson (1963-1968) caused an uproar when he lifted his beagle Dukie by the ears for a photo opportunity. See YouTube footage of Caroline's pets at
"Richard Nixon probably saved his vice-presidential candicacy ... with his impassioned speech about his wife's cloth coat and his cocker spaniel, Checkers" in a 1952 television broadcast, wrote Don Moser.  When Nixon became president (1968 -1974), a French poodle, a Yorkshire terrier and an Irish setter roamed the residential wing. See YouTube footage of this part of Nixon's speech at http://www.youtube.com/watch?v=XhQD2UFCIbY .
On Saturday Night Live, comedian Chevy Chase often spoke to a stuffed effigy of Gerald Ford's (1974-1976) golden retriever, Liberty, when playing the president in sketches.
Georgia girl Amy, President Jimmy Carter's (1976-1981) daughter, named her dog "Grits." Ronald Reagan was a horse-lover who did not get his sheepdog, Rex, until his term (1981-1989) was almost over.
Canine philanthropist Millie, George Herbert Walker's (1981-1989) springer spaniel, had a bestseller, Millie's Book, that raised $900,000 for literacy programs.
 Updated from "Top Dogs," People Weekly, January 19, 1998.
 "AARP TV: Presidential Pets," YouTube http://www.youtube.com/watch?v=0d2GvRoEmXA
 Babbitt, John S. "White House Pets Come in All Shapes and Sizes," Stamps, December 3, 1994.
 Moser, John. "All the Presidents' Pooches," Smithsonian, June 1997.
NOTE: Unless specifically cited again, information for this article came variously from the five cited sources.