Bring back the B-Class and C-Class buttons to set the range. I would seriously miss this feature if it were not available. Even better would be custom buttons for ranges. I am migrating a 500 networks from /24 to /22, and having a custom /22 button will save me a lot of time.
 Bring back the "Paste IP" button from clipboard ... where would I be without it :)
NB: The above 2 features allow for RAPID 3 click scanning;  Paste in the network address  click Class-C  click scan.
 Built in SNMP functionality would be awesome. You could include the ability to enter a selection of SNMP community strings, and return common info (model, location, contact, etc) for all hosts that respond to one of the strings. You could even allow for custom MIBs to be requested. On the interface, I would return the node with a "+" sign to indicate "more info available". Click the "+" and the node expands downwards (like windows explorer opening a folder) and shows the SNMP details.
 Integrated PSLOGGEDON.EXE type functionality to tell who's logged onto WinXP PCs.