What are the alternatives to Activity Monitor that will summarize cpu time over time?
I'm a huge fan of Bjango's iStat menus, which allows one to conveniently place various monitors (CPU, disk usage, network up &amp; down, battery, memory, temperature sensors...) up in the menu bar.  Each one can be pulled down like a menu for additional details.  It's a $16 app.  You can try before you buy.

Edit:  it looks like they have released another monitoring application called MiStat that is a separate app instead of living in the menu bar.  This allows them to place it in the Mac App Store.  It's available for a $4.99.  



Edit: I'm sorry, I must have not read your question carefully enough before I posted.  I do not know of any GUI tool that is able to aggregate CPU time being consumed by several similar processes as you describe.   The best idea that I can think of would be to write a script that wraps the top or ps commands and adds up processes that match a regular expression.   This strikes me as a market opportunity for a nice utility.   Could you describe a little more of how you would like such a thing to behave?