2weeks strong...BUT

[Owlie]

Welcome to TE!

My question to you is: What do you want to do, and what do you want to ride on? Roads? Paved rail-trails? Unpaved paths? Do you want to do really long rides, or shorter ones to run errands? Both? At some point, would you want to race? Charity rides? Once you've got those answered in your head, then you can start looking at what kind of bike you want. (Road bike? Flat-bar road bike? Hybrid? Hard-tail mountain?) I spent $750 on my first "grown-up" bike, and I'm probably going to spend a heck of a lot more on my next one.
Since you sound like you're not quite ready to take that big a plunge (yet ) consider buying used. You'll get a lot more for your money that way. If you want to buy new, look at Trek and Giant, which tend to be good bang-for-buck manufacturers.
Go to a reputable bike shop, and tell them what you want to do. They'll be able to suggest specific bikes for you and let you try them out if they have one on the floor.
Bike shopping is fun. Enjoy!