I'm in the middle of my senior year too and have finished getting my applications out. I applied to 7 schools. It's wierd, most are in the North East (Boston, NYC), but I also applied to UofA and ASU and even UC San Diego. So I'm either going to be in one corner of the country or another... hah
I know I have a warm fuzzy feeling for pretty much all the schools I applied too. My favorite is Boston College though, even though UCSD is nice too. My parents made me apply to some schools I know are way out of my reach too, but I haven't really become too attached to them so when I get my rejection letter I won't be too sad.
Like you I want a school in a big city or right outside a big city, but I don't really care about student population that much. I'm not really picky though so I think that works to my advantage. Plus, my high school is huge, over 2500 kids, so I'm used to big groups.
Good luck to you. It's all up to you in the end though. My best advice is go visit some schools this weekend (3 day weekend for MLK day), and HURRY UP AND GET YOUR APPLICATIONS IN!!! Applications for most schools are due very shortly or should already be in!