In many cases, you can go to Add-Remove Programs and quickly find Ask.com listed and do an uninstall. In other cases you have to study the list of programs very closely and you'll see a reference to Ask.com in one of the Titles, and you can just uninstall that.
But in other cases, some unscrupulous vendors hide it so well that they don't even list an Uninstall for it.
Here is how I was able to completely get rid of it in one case.
I first did a registry search for Ask.com and ultimately found an entry this reference:
I then tried to delete the folder C:\Program Files\Ask.com\ but it wouldn't let me.
After looking around inside the folder I found Updater.exe
Then I looked in Task Manager and found this Updater.exe process was running, so I killed it.
Then I could delete the contents of the C:\Program Files\Ask.com\ folder.
This gets rid of the Ask.com Toolbar, but I suggest you use your favorite Registry Cleanup tool, such as CCleaner, to get rid of all of the references to it in the Windows Registry.
I know this is all about money. Vendors looking to make a quick buck take money from Ask.com to bundle their toolbar, but this kind of thing just makes me loose respect for all of the vendors involved. This is akin to malware in my opinion.