well, call it a short time memory, but I have a few from the last US Open.
1) Venus vs Serena final
2) Martina Hingis vs Lina K., yes Martina is one of my favourites and I was happy she won, but Lina played one of the worst matches I have ever seen a player play

Then from other tournaments
Martina vs Monica Key Biscayne, again my favourite winning but it was painful to see Monica losing like that.
Davenport Hingis AO 2000, bias apart, it was really only Davenport playing there until 5-1 in the second set.
FO 99 final
Wimbledon 98 final, Novotna vs Tauziat. Novotna was one of my favourites and I had one of the greatest satisfactions since I follow tennis with her winning Wimbledon finally, but really the way they both played they should have declared the title vacant
Anna vs Sidot Wimbledon 2000. It was painful to see Anna, she didn't have a clue about what to do.
Capriati vs Serena Canadian Open, I've never seen so many errors from both sides in my life.
I can't think of any more at the moment