Medcin from Medicomp has long been a leader in this area with their clinical Medcin terminology. Here is an example of their user input screen. I learned a lot about clinical user interfaces by reading Medicomp's materials. Some EMR vendor web sites include good screenshots of their user interfaces. I have noticed a lot of vendors have utilized a "Medcin-like "clinical observation documenting style.
Microsoft has just released a Guidance document for clinical terminology matching for a clinical user interface, which is part of their CUI project: http://www.mscui.net/
They have put together some nice guidance documentation on clinical user controls. I have done a lot of reseach in this area and it is hard to find any comprehensive guidance information regarding clinical user interface development.
Although Medicomp has some good information on their website which includes some nice powerpoint presentations with good screenshots, Microsoft has taken it to the next level. They have made a significant contribution to the clinical IT open-source community by releasing this set of comprehensive clinical user interface guidance documents.