I sort of do two things which result in strange looks and girlish squeaks of "You sound like a guy!" from my brother (though I don't know how well I'd fare in real life). I sing low a lot, some pop, some musicals, etc., and I've noticed my range going from the traditional alto (and soprano when I can bothered) range to baritone (and the top bits again, when I can be ar*ed, which is rarely). So that's fun.

Then, when I want to sound less female, I relax my voice as I would when I want to hit the low notes, but then just talk normally. I'm not trying to pitch my voice lower, per se, I'm just trying to relax it so it comes out with a slighter deeper resonance, or something. Essentially, I'm just talking lazily, not bothering to tense everything up to its normal state, but keep everything loose. It ends up sounding - in my head, anyway - no lower than normal, but it sort of has a sharper low edge to it. Of any of that makes any sense.

I found...
- Every You, Every Me (Placebo)
- Do you hear the people sing? (Les Mis)
- No place like London (Sweeney Todd)
- You spin me round (Dead or Alive)
- I kissed a girl (Katy Perry) - sung down the octave
- The Sailor's Arms (Doug Anthony All-Stars [aka DAAS])
- Throw your arms around me (DAAS)
- Mozart's Requiem in C minor
- Phantom of the Opera (particularly Raoul and the Phantom's parts)
...really helped me to drop my range and develop an "edge" to my voice, which, as I said, may or may not sound masculine, but apparently comes across as less feminine.