Icons play a major role. What you have to pay attention to is to have clear and unified set of icons throughout the whole UI. Eclipse is a nice sample for that.
Finding the appropriate icons is however not always that easy. But I found two search engines which may help you:
You find there a rich set of different icons structured. There are a lot of the icons which are used on the Eclipse UI. They are simple but still nice-looking and clearly understandable. Here is a sample of searching for the keyword "save".
Another search engine I found today is ICONLook. Icons there are more Microsoft style. There are a lot of Windows Vista glass style icons.
Here is a sample of searching for the keyword "save".