I don't have time to read all the replies, so my apologies if I say anything that has already been said.
1. Buy quality. You'll find out what quality is by reading SF and some of the recommended blogs. It's always better to have a few quality things than a bunch of crappy things. This goes for anything.
2. Don't fall for trends. For God's sake, don't be that college student with desert boots, selvage denim that hasn't been washed in a year, some really ugly ironic t-shirt or sweater, and an American Apparel hoodie. You'll look ridiculous; like a poster boy of the latest month's trend. Buy classic stuff that fits, will last, and will be something you can wear in 5-7 years.
3. Dress your age. Don't be the guy who wears a tie and loafers, but is 20 years old. At the same time, don't buy ironic t-shirts and ugly sweaters.
5. Find a good tailor. This will do more for you than any other tip you can get. Get stuff that fits you pretty well, then take it to a tailor to have any things that need to be adjusted worked on. Pay attention to the length of sleeves and pant legs, as well as shoulders and chest areas on your clothes. You don't want slim or baggy clothing - you want things to fit you well.
Lastly, remember that girls in college don't care about how well you dress after a certain point. Wear stuff that fits, and put in a minimal effort, and you'll be fine. Don't look like a slob, clean your room, be hygienic. In the end, if you accomplish that, that's your baseline in terms of appearance. After that, do the things that girls do care about - be polite, be considerate, be interesting, be smart, be charming, be witty, be funny, be all the things that actually matter. Know that women don't care about how we look in the same way men care about how they look, so don't obsess over this clothing stuff. Note, I'm only putting this point about girls here because you're in college, and you probably aren't married, so you probably care about such things.
Also, I have to say this as a graduate student - please note that you should be paying attention more to your classes than what you wear. This time in your life matters a lot.
As for the basics, you need:
1. A nice blazer, preferably navy blue, or something khaki or grey.
2. Good straight-cut blue jeans.
3. Khaki pants.
4. Mid-gray wool pants (something like a tropical wool, if you need something to go to interviews or fancy events on campus).
5. White and light blue oxford shirts
6. One dress shirt, either white or light blue.
7. A tie, either something solid or striped.
8. A grey crewneck sweatshirt
9. Cashmere v-neck sweater (light gray or camel/oatmeal are good colors).
10. Plain white, or monochromatic, sneakers
11. A pair of captoe shoes, preferably oxfords (for when you go to nice events).
12. A pair of chukka boots or plain toe derby (for everyday wear)
13. Belts to match shoes (try to get the color to match)
14.. Plain t-shirts - get white, navy, brown, and heather grey
15. After this, you may need one or two casual jackets. For cold weather, you can get a peacoat or duffle coat. For less cold weather, you can get a Harrington jacket or field jacket.
16. Depending on the weather, you might need things like overcoats, gloves, scarf, raincoat, or rainboots.
After that, get some other button up shirts - things in solid colors, or bengal stripes.