One of the best knitting tips I ever got...
Circular needles aren't just for knitting in the round! They're also GREAT for flat knitting (back and forth) because you don't have the long straight needles sticking out past your elbows! It's like working with smaller, more manueverable needles, much more comfortable.
And you can choose a length that's appropriate for your project. I'm working a scarf on 16" circular needles right now. If you're doing something bigger, like a sweater front or back, you can use a longer set that will accomodate all of your stiches and the needle itself still fits in your hands.
I rarely buy straight needles now unless I can't pass them up because I like them aesthetically. Rosewood, nicely carved tops, unique...needles that look good in a cup on the desk. That's the only drawback of circular needles...they don't look good in a cup on the desk.