Modernbill is a pretty nice all around solution. Another is UberSmith.
WHMAutoPilot is getting some hype now but they currently have a tarnished rep, even more so than MB, with the delay their stable release v3. WHMAP also said that a demo would be up shortly and it's been weeks now. It would be hard for me to so suggest WHMAP as a workable solution for your company. However, many use them and praise them. Updates however are very slow coming. IMHO (of course)