I usually recommend the AutomationDirect C-more for simple applications. It is easy to learn, easy to use, and inexpensive. My personal favorite HMI is the Red Lion G3 series. It is also easy to learn and use, and has lots of advanced features, such as programming, that makes it very flexible. It is more expensive than the C-more, but the software is free.
The Delta downloads web page includes example projects for the C-more and G3 HMIs. These projects are already set up for communicating with an RMC: http://www.deltamotion.com/dloads/downloads.php?category=rmc70&subcategory=Examples
Other HMIs can be used, of course, but they must fulfill the following requirements:
Supports one of the following communication protocols:
- CSP (DF1 over Ethernet)
- Supports 32-bit floating-point numbers. I have found that some HMIs support 32-bit floating point numbers partially, but not in the critical areas needed for easy use with RMCs.