Visible crew/equipment: When Dewey yells for Lois because the bow was put on the present, if you look to the left of Lois, you will see a crewmember kneeling down, handing Lois the Red Dress, who is holding a bucket of water. He quickly gets out of the camera's view. [This is on the DVD of the first season. Someone said on the audio commentary that after catching it, they deliberately left it in to see if anyone would spot it. It's still a mistake, but that's why it's there.]
Star-Crossed Lovers and Other Strangers - S1-E16
Visible crew/equipment: When Rory asks Lorelai to call Emily to get her out of Friday night dinner so she can celebrate her and Dean's 3-month anniversary, a boom mic drops into the shot as Lorelai stands to get the phone. (00:07:05)
The Perfect Thanksgiving - S2-E6
Continuity mistake: The hospital where Nurse Kathy works isn't the same one she worked at in "Episode Eleven" and "The Test".
Continuity mistake: Larry is sitting on the couch close to the arm, drinking wine. Susie sits down, making Larry spill his wine on the couch. Larry is now sitting in the center of the couch. (00:11:49)
Jane and the Truth Snake - S2-E5
Continuity mistake: When we first see the guys at the pub, Jeff takes a swig of beer and you can see that his glass is almost empty. After a few seconds of conversation, he takes another sip and the amount of drink has significantly increased. (00:06:00)