In general, most places that I've been in during my 30 year career have had managers and supervisors generally wearing golf shirts and khaki pants or something similar. This is for places that have no real dress code other than clean, in good repair and not offensive.
I would take a look around the company and see how the rest of the team leaders dress. Regardless of how the geeks dress, you're going to need to peddle influence in order to get your budget and policies passed. The better you dress (without overdressing your higher level managers, the more respect you can garner from people that have no clue about IT.
Check out what your manager and his peers wear and go even with that or *one* step lower. If the company president wears jeans and band tee shirts, it don't matter none...:-)