Check Battery Life before you buy. Take the claimed life and take off 20% as a rough guide. You can reckon on having to replace a battery every three years if you use the laptop every day on battery power.
Otherwise I`d say that most laptops these days will do what you have stated, even the cheap ones so start to think practically. A 15" monitor is a minimum spec and avoid a widescreen. (They`re great for DVD`s and spreadsheets but lousy for Word documents,Powerpoint etc - you keep having to scroll up and down)
I use a laptop all the time for business and you will benefit from a standard mouse and keyboard - put simply a laptop keyboard and touchpad are not the most ergonomical for prolonged use. I opt for a wireless keyboard and mouse set up - If I`m only going to use the laptop for short periods I use the laptop keyboard and a retractable mini-mouse. I don`t carry these about with me all the time, I tend to leave them where I am normally going to be based. When I do take them with me I use a small rigid framed case on wheels. Enough for laptop, Wireless KB & Mouse and plenty of room for files.
Lastly choose a laptop with plenty of RAM - minimum of 512Mb preferably 1 GB and a good speed processor. AMD Turion (?) or Pentium Centrino. I really don`t worry about the weight too much - the trolley bag sorts that out.