Worst Gift?
Wiper blades and new car smell for Rachel from Joey/Chandler takes some beating. (at least you can drink the soda, and the toilet seat covers and condoms have a use!)
other notable mentions
Travel scrabble (chandler to Rachel)
Book ends (Chandler to... Phoebe/Rachel?)
the pen that also tells the time (Joey/Chandler to Kathy)
Any others?