You can do this in Nero. I didn't see it at first either because it is not available unless you use mr. wizard.
Tested on Nero 5.5, not initially using mr. wizard:
Here is what you do:
start Nero, select CD-ROM (ISO), L-click the New button, drag files from any hard drive or CDrom into the compilation window, L-click the Write CD button at top, when the Write CD windows appears press the mr. Wizard button, select the Create Image checkbox (should have a checkmark in it), click the Burn button, a dialog box will ask you what name, location and image filetype to burn to, select iso if you want iso and give it a name and location, then click the Save button, and there will be an iso or nrg image file in the location you had chosen.
I like having full control over the details so I didn't see this at first until for the fun of it i clicked the wizard option.