How do you keep your data tables simple?

Our company is trying to make our website simpler and easier than our competitors, and one thing that's difficult about that is our data. A big table of data is shown on most of our website's pages, so it's essential that we make this simple. We've tried to slim down the table by removing unnecessary information but from a business perspective, a lot of it needs to be kept there. Here are a few things we've done so far:

• Add collapsible rows for things which are "sub-tables". Imagine a list of companies, and each company has a sub-table for a list of employees; that sub-table is a collapsible row that expands beneath the company's row in the table.
• Add tooltips for more detailed information about things such as cost if there any complications.
• Add modals/popups for a very, very detailed breakdown of that row which are opened by clicking on a link (using the row ID).

Now I'm at a point where I see a table which can't have too many things removed. We have important things such as customer info, prices, edit/delete buttons, checkboxes etc. that can't really be removed.

Do you guys have any tips for keeping your tables simple? Or do you have any little tricks you use to save space/columns with your tables?