Tips to stop heat on huge south-facing windows?

I have most of our windows facing west and surfing the summer, there is so much heat entering the rooms via the windows. We have blackout cellular blinds and it helps a LOT when we keep them closed or mostly closed during the super sunny summer days.

Adding shading (awing, exterior california shutters, etc) is best.
If you can't do that, then you can add solar tint film to reflect the heat/light.
Next would be a white blinds or roller shade.

My primary bedroom is also south-facing and we get loads of sunlight. When we moved into the home we had Hunter Douglas cellular shades (black out) installed by the previous owners. They did a great job at blocking out the light, but once in the sun for 30+ minutes they started to absorb the heated and just radiated it inside the room.

We've since changed to Roman shades (black out) and so far they are doing much better with respect to heat, but admittedly they do let more light in.

I would say wood shutters are probably the best overall option if you're looking to minimize heat.

Note that you can also apply a window film which will help to minimize the heat/light.

Window film would be inexpensive to install if you DIY. I did it on my bay window that has one big 4'x5' pane. It was about $85 for the window film and you'll need a good utility knife, squeegee, long straight edge, and spray bottle. It's definitely a two person job to ensure it goes on smoothly without crinkles but can be much cheaper than installing shutters, awning, or cellular blinds. But with really big panes, you have to consider that there will be a seam. It's a pretty noticeable reduction in heat, retains visibility to outside, and still allows some light in.

We put shutters on our two story family room windows to keep the heat from the sun at bay.

We moved into our home at the beginning of May and by the time the sun came around to those windows the temperature in the house climbed 10 degrees almost instantaneously.