I know of this gemarah teaching (see also Midrash Rabah 12:2) about Bereshit 2:4 which teaches that the phrase: 'Eileh toldot hashamayim v'ha'aretz b'hibaram' could be read as 'b'Hey baram', that HaShem created this world with the letter Hey.
R. Yitzchak Hutner (in Pachad Yitzchak to Sukkos) writes that the reason a "hei" was added was because Avraham was becoming a new creation, so to speak - being fashioned from new.
From these teachings it seems to me that the letter Hey represent 'creative power'.
Well I can't remember from where but I remembered comming across this teaching about Adam HaRishon being created with the letter Hey as well, that HaShem breathed with the Hey - the divine breath - into his nostrils the breath of life. That HaShem formed man of the dust of the ground and with this breath he became a new creation; a nefesh chayah. Anyone familiar with this teaching and knows it's source?