For starters, it will really depend of exactly what you want from a laptop - Power over portability or battery life over performance; screen size over weight or multimedia performace over battery lefe etc (you get the gist)
If you are wanting to use the laptop mostly on the plane while flying then with available power supply, battery life is not so important. If however, you are going to be using it in the "field" then you will need to sacrifice performance for longer battery life.
Also, if you just want basic word processing and email facilities then there are a lot of products available and well within your budget. If you want networking, built in wireless and the suchlike then your budget starts to look a little tight.
The best thing to do is to see the products for yourself. PC World (I shudder to mention) has a fairly good range on display and you can get a feel for them. As to brand names, a large number of laptops are made by the same few manufacturers and then simply "rebranded". Go with a firm you like a product you feel happy with.