I have been using opedcl before it went open source when it was called objectdcl
It blows AutoCAD dcl away. Once you get into to it you will never go back to dcl.
There is a bit of a learning curve but it is well worth it.
The forums on opendcl.com are a great help.
There are many tools to use and you can easily place them on a form anywhere you want.
Opendcl uses an ARX file so it has to be loaded into AutoCAD.
I made a generic load lisp file to load the project and arx files into AutoCAD so I just copy the file and change the project name and include the file when I make my VLX file
You can also encode the dialog box file so it cant be read by anyone.
The drawbacks are:
The arx file is version specific meaning when AutoCAD compiles in a new version of c++, you have to wait for the opendcl guys to issue new runtime arx file. But they are usually on top of things so the wait is never to long.
Run time files must be distributed with your program.
Opendcl is an open source program so it is constantly changing, adding new things and fixing bugs. There are issues when you have used the software for while then get the newest release and then you have issued with your code because of a change or fix.
In my opinion its worth the hassle, you just have to stay on top of it.