In Shmuel Aleph Perek Aleph Elkana is refered to as Ish Echad before his name is given. The Midrash, according to Meam Loez, says that the Echad means Singular or Special. I was wondering where else in the Tanach is it used this way?
Malbim (I Shmuel 1:1) believes that "ויהי איש אחד" specifies that this man is unique in purpose (מיוחד). [He gets this idea from a midrash that I unfortunately cannot find.] Here, Elkana is "uniquely destined" as Shmuel's father.
The other example Malbim brings is from Shoftim 13:2: "ויהי איש אחד מצרעה", referring to Manoach. Manoach was not necessarily a great man, but he too was "מיוחד" to be Shimshon's father.
It's not just with "ish." Since a singular noun obviously means there's only one of it, then whenever the Torah uses the form "X echad" (or "X achas") it tells us that there is something special about the referent. As one example, the Gemara (Megillah 28a) points out that the expression "ha-keves echad" (Num. 28:4) teaches us that it has to be a "unique animal in the flock" (i.e., the highest quality).