Welcome to the club!
If you go to WalMart, you can get a small fan like I have for
$12. It plugs in your cigarette lighter and has a clip so you can mount it somewhere. It doesn't really do much for cooling, but it does at least give you some airflow.
I also got one of
these recently. It's basically a small swamp cooler. It has a sponge that you wet, and the system brings in air, cools it with the water, and pushes it back out. For a small device, it actually does a pretty good job of cooling air. The sponge lasts about 30 minutes - an hour depending on how hot it is and what speed you have the fan on (which is enough for me, most of my drives are 40 minutes or less). It runs off 4 AA batteries or USB (you can get a USB adapter for your cigarette lighter for like $10 at WalMart or AutoZone). There are some "generic" cheaper chinese models if this if you want to go that route, but like with most stuff the quality isn't that good and it doesn't cool air as much as the real thing (at least from what I read online). The best use I found for this is actually sitting at red lights. When I'm moving and I got the windows down it's not that bad, but it's the sitting at red lights forever it becomes warm. That's when I turn this on and use it to stay cool, and then shut it off when I start moving again and can use just the wind going by.
Other then that, just basic stuff. Keep plenty of water bottles in your car, use a sunshade while parked outside, and if you can maybe adjust your schedule so you can drive during early morning and later at night (that's why I've been staying at school a little later recently, it's cooler out when I leave).