Summer is over, all right. The box office was sluggish this weekend, though both Keanu Reeves and Renée Zellweger should have smiles on their faces this morning. Their movies, "The Watcher" and "Nurse Betty," respectively, opened strong, despite lousy reviews for the former and sharply divided ones for the latter. The weekend race, according to studio estimates: 1. "The Watcher," $9.1 million 2. "Nurse Betty," $7.3 million 3. "Bring It On," $6.5 million 4. "The Cell," $3.5 million 5. "Space Cowboys," $3.3 million 6. "What Lies Beneath," $2.9 million 7. "The Original Kings of Comedy," $2.5 million 8. "The Art of War," $2.4 million 9. "The Way of the Gun," $2.2 million 10. "Highlander: Endgame," $1.8 million