Shieldbreaker is a defense against all the other swords except Woundhealer. Farslayer eventually was destroyed by Shieldbreaker. In the Last Book of Swords, Shieldbreaker destroyed all the other swords remaining except Woundhealer, since you couldn't consider Woundhealer a weapon and Shieldbreaker got destroyed instead. The last book was an easy way out for the author anyway; wasn't that good all things considered.
Grayswandir the Nightsword, but don't forget Werewindle the Daysword. Actually both swords are Spikards like Merlin's ring. You don't find that out unless you read the Amber short stories, however. Zelanzy never finished them before dying, so that sucked.
By the was, is the Heaven sword and Dragon sword thing the final part in the Condor legend series?
Where can I get that yin yang thing someone was talking about? It sounds interesting.