In almost all cases, I have seen the word "Yerushalayim" spelled like this: יְרוּשָׁלַיִם. However, sometimes I have seen it spelled like this: יְרוּשָׁלִַם, missing a י between the ל and the ם. Is this just a misspelling, or is this really a true variation?
[Note: This "misspelling" is made in my Siddur Tehillas Hashem and my Machzor Hasholeim from Kehot. Both are all-Hebrew. Pictures are provided here for ease of access. I also remember seeing this spelling in the Stone Tanach somewhere in Psalms, but I cannot find it again.]