Jennifer Aniston and John Mayer Photo by: Lester Cohen / WireImage; National Photo Group

Sunset Tower Hotel was the place for star gazing Monday night, when Jennifer Aniston and John Mayer dropped by for a late-night meal.

"They were positively glowing in the candlelight," an onlooker said of the couple, who took a corner table in the dimly lit Hollywood landmark, where the couple is frequently spotted. "You could see her classic 'Aniston smile' on her face."

The on-again couple - just back from their jaunt to New York City - talked closely in low tones.

But they did take time to chat with another celebrity couple, Nicole Richie and Joel Madden, who were dining nearby.

"There was a lot of excited talk between the two girls," the onlooker noted, "with Nicole's head bobbing up and down as she talked to Jen." (When Richie star-exited the restaurant a short time later, she gave an "exaggerated, very happy wave" to her new Friend.)

But for most of the night, Aniston, 39, and Mayer, 31, only had eyes for each other. "They were very happy and goofy," the source added. "They seemed to revel in their privacy."