You should consider the upgradability of the Mac Mini - you can buy new updates and have a screen to use. The mini IS due for updates, and a leading rumor in March said the mini was being gutted and re-engineered from the ground up. You might see them released in January if the rumor is true.
I suggest waiting just 3.5 more months until MacWorld 2009.
The iMacs are very nice, though, and so easy to use and carry around. If I was in college I would get an iMac so there is no clutter to carry around. When I was in college I had the crappiest Apple II+ and it was a method to transport around. Kids have it so easy these days.
...then again, if I had a monitor in my room and a monitor at home, you can just disconnect the little mini and tote it home on weekends in college. If you are mildly ambitious you can crack open those minis and upgrade the drives and memory yourself. I am hoping the updates (if they come) will make the mini slightly bigger with a regular drive inside, so we could have 1TB interior drives.