First of all, there are many types of crops you can grow, each with it's own special attributes (and taste!). You can grow only some during certain seasons (once you have the greenhouse, though, you can grow everything except strawberries anytime you want). Here is a small table that will help you out:

crop	price (buy)	price (sell)	season	growth (days)	regrow?
Turnips	200G (bag)	60G each	Spring	4	no
Potatoes	200G (bag)	80G each	Spring	6	no
Cabbage	200G (bag)	90G each	Spring	7	no
Tomatoes	300G (bag)	90G each	Summer	9	every 3 days
Corn	300G (bag)	120G each	Summer	13	every 4 days
Eggplant	300G (bag)	70G each	Fall	7	every 3 days
Strawberries	500G (bag)	150G each	Winter	6	no