For a fighting knife, it's hard to beat a KaBar or Camillus Marine Corps fighting knife. They are tough as nails and work really well when you need a big knife. Many other knives out there, but avoid the quirky and go for solid. A smaller "utility" knife will work just as well for a self-defense knife and not attract as much attention.
Whatever you choose, get good steel. I personally like a good 4"-5" carbon steel blade (takes an edge easily, holds an edge well), but a good tool steel blade is a great knife (harder to sharpen, but hold an edge until Judgement Day). Here is an example of a good utility/field knife:
http://www.eknifeworks.com/webapp/eC...=10&SKU=ON8620