Welcome to the forum and to the crazy biking habit!

My advice, forget brands for now; that's less important. You need to be thinking about what style of riding you want to focus on, what features/abilities you want in a bike, and what your budget is (for the bike AND for all the necessary startup accessories).

Some questions to think about for yourself (and answer here if you want feedback on bike types/brands/models that we'd recommend):

What type of terrain is my primary interest (mountain single track, groomed double track/packed trails, paved trails, roads)?

What types of terrain do I want to be able to handle even if they aren't my primary use?

What is/are my cycling goal(s) and what is the priority order (commute, commute to school, road group rides, fitness, racing, mountain biking, tricks, etc)? (This question will actually feed into a list of more specific questions to ask yourself later!)

What is my current fitness level and difficulty of terrain I plan to ride on and what equipment do I need to make that workable? (we can help with the second part)

What is my budget?

What are my storage options (inside most of the time, needs to be locked outside, needs to be locked outside sometimes, security level of locations, etc)?

After you get those somewhat sorted out in your head (and it's ok if some of the answers are "I'm not sure, but I'm thinking maybe....") you can head back here or to your LBS (local bike shop) and get lots of good suggestions for bike types and brands to try out and some other questions to think about.