A Quick Word on User-Interface Design
Excellent user-interface design isn't that complicated. It is not my intent to take anything away from experts in this field with their HCI, human factors, cognitive psychology, etc. degrees, I simply don't think it takes a PhD to design usable sites and web-based interfaces.
As someone who has evangelized user-centered design and web accessibility good user-interface design has simply been a must. It doesn't matter what functions the web-based service has or how robust the data is if the user can not intuitively use it. Bottom-line: if the user can't use it, it's useless.
Now on the web this become tricky as you have a single user-interface that every end-user group with their individual thought process must use. By simply understanding your users (who they are and what they are there to do) and understanding some basic and fundamental online behaviors patterns and theoretical UI and design principles a sound and usable site design can be obtained. Then by running this design through some usability workshops the subtle nuances should be vetted and a web-UI with strong visual hierarchy and an intuitive navigation system arrived at.