Congrats on getting a DSLR. Here is my shoestring budget recommendation.
1. You have the 50 1.8. Perfect for portraits and thin DOF photography for the 600.
2. You have the 18-55. Look at Panoramic photographing. http://www.ptgui.com/ is a good start. This will get your landscape and architectural shots but will require work stitching a few pictures together. You can do this also with Photoshop (or a free stitching program), which I am sure you can get free access to in college. You would need to get a sturdy tripod w head (dad's closet?) and buy or make a DIY camera bracket that allows you to spin your camera about the nodal (entry) point. Home Depot has "l-brackets" that will do the job (search you-tube or the web for DIY). If you are resourceful enough, you may get away just spending 20 bucks on l-brackets and screws. Maybe you will need to spend $10 on a level that sits on your camera hotshoe (ebay) or maybe it is already built-in on your live view - check.
2. Now that you have extra money, go get a flash (search Yongnuo flash on ebay). you can get it for 75 bucks or used for alot less. The flash will get you quality indoor shoots at college parties by bouncing the flash off walls or ceiling. Also great fill flash for portraits.
Video is a whole new ballgame. I think the new t4i has auto focus. The older cameras, I think, are basically manual focus. This make video more difficult than a dedicated video camera. If you truly need the cinematic quality that the DSLR offers, you will be spending some $ to assure your subject is steady and in focus especially at low DOF. Or use your 18mm and keep the aperture smaller than f8. If you are going low DOF effect, read up on the web. Cheapest way is using a monopod (or use you tripod with one leg) and a jar opener for a steady focus handle.
3. So now you have $350 to spend on the Canon 70-300 IS. I think you can get one used for $300-350.
Or if you can find one, get the canon 70-210 f4 for $100. another option is the older 70-210 f3.5-4.5.
Both are very sharp for the price.