Less Annoying CRM has a filtering option you can use to find records who are not in a specific group. If you go to the Contact list, you can select “Add a filter” under the “Filters & Sorting” section in the page menu. In the dialog that appears, choose “Group” and then select “Show contacts that are NOT in the following group(s)” in the dropdown below.

You can then tick the box to the left of the desired group(s). When you apply the filter, it’ll pull up only records that are not in the selected group(s).