Suggestions for a new bike owner?

Hi ladies; I'm having a hell of a time picking out a new bike, can any of you help?

I've been riding a 3 speed cruiser bike that someone lent me last summer. It was miserable to ride up Cincinnati hills. In general it was heavy and slow (though very comfortable to sit on).

I'm tired of staring at my boyfriend's back when we take rides together. I want something faster and lighter than the old cruiser (though I think that is EVERY bike)

I ride in the city and am in no way an experienced rider. I don't know if I could gets used to a bike with low, curved handles.

For all you riders who are somewhat like me: what bike do you love? Just as important, what bikes were tempting but turned out to be not so great??

Just to add more complication: I'm a poor grad student on a tight budget ($200 but could maybe stretch it to $350). So I'm searching craigslist and trying to be patient for the right one to come my way. I've seen a Trek Navigator (another poster on this site said it was heavy for hills), Trek 7300, haven't seen any of the Trek fx yet. My friends have gotten awesome used bikes for $70-100, I don't want to be a sucker.

I am learning so much about bikes as I read these posts. What components should I be looking for that fit my needs as I search through all the used bike listings (since I might not be able to look for a specific brand). Things like frame, suspension, shifters; I'm just now learning what these things are so I'm going to look up any parts you mention for definitions and more information.

Thanks so much for your help.

For city riding, definitely no suspension, it will just cut into your budget.

Although i'm not suggesting you go get a road bike, I am certain that you COULD get used to the handlebars, if I could do it in my 50's so can you. The trick is to find a bike that actually fits you.

On your budget, all I can suggest is craigslist and garage sales.
and if you have time, go ahead and test ride bikes that might not be what you want. You can learn a lot that way.