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I do all manner of soups and stews in my slowcooker. Just be sure to brown any meat you're going to use the night before, because nothing browns in a slowcooker, and there isn't nearly as much evaporation, so the amount of liquid may have to be adjusted in your favorite recipes. Knowing that, basically any soup or stew can be made in a slowcooker...set it to low before you go to work and it's done when you get home. Especially wonderful for bean and grain soups that benefit from that slow heat and get really, really tender (split pea, beef and barley, beans and hamhocks...yum). Which brings me to the other selling point: One can use a far less-expensive cut of meat when one is willing to cook it "low and slow". Things like hamhocks and lamb or beef shanks do really well. The only thing I tend not to put in my slowcooker is pasta, because it just gets gummy and disintegrates...if you want to make something like a minestrone, just add some pre-cooked pasta when you get home.
And as far as pre-cooking things, pasta is a good place to start. Without sauce on it, it keeps really well in the fridge, and one can easily heat a sauce really quick when one gets home. Precooked rice is also good for that..do some cooking on the weekend and stock your fridge.
As far as make-aheads, you can't beat the "lowly" casserole--and it's frugal. Just assemble the ingredients on the weekend, cooking any meat, and put the casserole together. Pyrex bakingware makes a glass casserole dish with a plastic lid especially for freezing/refrigerator storage...when you get home from work, just remove the lid, replace it with foil, and toss the whole works in the oven for an hour.
Sorry for the wordy post, but I was a bartender working odd hours for years, and couldn't exist on fried bar-food, so I started slow-cooking and pre-cooking out of self-defense...lost 15 lbs. doing it, too...and the wonder of casseroles and soups and stews and such is that, generally, they make the best leftovers, so don't worry about making too much...just take some into work for lunch the next day.

I wanted to respond but @rosezilla said it all! Love my slow cooker!

Cooks Illustrated has two cookbooks I definitely recommend, one is Cover and Bake, and the other Best Make-Ahead recipes. You could borrow them from your library if you don't want to buy, or if you're a member of their website you could probably find most of the recipes there and many of their regular recipes have a "How to Make Ahead" paragraph at the end.

They also have a couple Quick Recipe books if you're looking for meals you can put together quickly.

The other option I would suggest is taking fairly easy recipes and doing the mise en place prep work before you go to work, chopping herbs and veggies, portioning out spices and ingredients, and then have everything ready to go so all you have to do is set everything up and cook when you get home.