Quoting Amydb:" I got the names on a baby name site called baby2see.com and it gave me all those spellings and meanings. ... [snip!] ... I also like madalynn. We shall see. Plus the middle name is rea.. all the spellings go with that so that doesn't help either."
Biggest rule of baby naming:
Changing the spelling doesn't make it unique. It just makes it a pain in the ass to deal with when explaining how to pronounce and spell it.
Stick with Madeline. It's a gorgeous name.
Oh, and one of my all time favorite baby name sites to look at is http://nameberry.com/
They have extensive lists of names and names that you might like.