IBM, all the way.
They're black and boring, but nothing beats it in terms of reliability and durability. I particularly like the x line, since they're the slim ones.
Right now, I'm using a HP desktop replacement, it weighs like 5000 lbs and is massive.. it hasn't given me any trouble yet but I just don't have the same kind of personal history with this company. There have been at least 10 laptops which have moved through my house in the last few years, and the majority of them have been IBM.
I would highly advise against buying Toshiba or Acer. I have a friend who constantly has to get his Toshiba serviced.. he met a woman at the service centre who actually lost her job over the laptop, as it had completely crashed and rendered all data unrecoverable, just in time for a meeting the next day at the law firm she worked at. Acer just makes inferior quality products, their pricing reflects that but it's better to get a nicer laptop that will last.