Give it a charge and see. If it holds the charge, you're probably good for another couple of years. If you don't have a charger, you need to let the car run for at least half an hour to start building up a full charge again. If your commute to work is long enough, start the car early, let it idle a while before going to work, and then drive it to work. Toss some jumper cables in the back just to be safe

If it keeps starting in the morning, you're probably fine.
If you think you'll need the battery to be good for more than just going to and from work, then you really should trickle charge it with a charger. Sooner or later it's gonna go though...
When my last car battery died, it went all of a sudden. The engine started freaking out, idling at 3000+ rpm as the car tried to maintain voltage and charge a toasted battery back up. I had been on my way to lunch, but I diverted straight to a parts store and got there before the engine quit or the alternator burned up. They don't usually go like that though...