Cracking the car windows open doesn't help much, just a few degrees usually unless you have them pretty wide open or have a strong cross breeze.
A sun shade is too much work for me. Plus, by the time I have it folded, the car is hot again and I'm sweating like a pig.
I simply put a towel on my car seat. The towel gets the direct sun, leaving the seat under it far cooler. Then I move the towel to the passenger side before sitting down. Makes a huge difference to the temperature of the seat (which to me is the most important part to keep cooler, but then I don't have ventilated seats) and you don't have to cook while folding those annoying sun shades. Lets me get the car moving ASAP to have the AC kick in.