Thinking about it i also think Signum will find a more than worthy opponent in Sesshomaru(Inuyasha) and despite the outcome she wil probably end up earning some respect from the all-mighty Dog Yokai. Laevatein VS. Bakusaiga will be an spectacular duel.
I also pitted her against Yue(Card Capor Sakura), Shana and/or Wilhelmina(Shakugan no Shana), Hiko Seijuro(Ruroni Kenshin, because the guy is just that awesome), Zenki(Kishin Douji Zenki) and others. For the crazy fights are Wolverine, Wonder Woman, Optimus Prime(yeah mimind get some crazy ideas from time to time) and the Hulk(which is a survival match for Signum of course as she tries to wear down the implacable monster).
So far i like to pit her against other heroes, i'm bad trying to imagine her fighting an spectacular battle against villains from other shows xDU.
Well, Galatea and Miria would make good opponents for her, too. ^^ My suggestions will also be: Princess Cornelia from Code Geass, Shiki Ryougi from Kara no Kyoukai, Oyuki from Lady Snowblood, Juri Arisugawa from Utena, Astaroshe from Trinity Blood, and Samara from Mass Effect 2. ^^;
Searching for worthy opponents for Signum in all of anime and other media(as Cypha isn't worthy ....at all):
Sometime ago(even before watching StrikerS) during a talk i pitted Signum against Teresa of the Faint Smile(Claymore) as two close and powerfull womens of sword and grace, and after a fierce battle we decided that Teresa will come out as the victor because of her insane intuition and lighning fast reflexes, it's like Signum's skill combined con Fate's super speed combined with the ability to predict the opponent's moves. Signum's insane defence and her own battle-forged abilities over hundreds of year make her also more than a match to the invincible Claymore Number 1 we accorded Teresa's victory by a really close margin and the possibility of Signum winning a rematch.