Road Bike as a College Student...

Also learn how to lock your bike through the frame & wheel and not just the wheel (or you'll return to the wheel with no frame attached)

Having a bike that is crappy looking compared to everything it's parked next to helps - you want the thieving toerag to ignore your bike and go for Tarquin Prendergast's sleek one.

Agree with the others, a second hand bike which doesn't look too flash.  

Whatever you take to University WILL be stolen, just buy/plan accordingly. I had to lock my bike up inside my student house because the thieves would break in during the night (more than once).

If you have the storage space I'd try and find a local re-cycle/ bikecycle type place and see what sort of beater you can get for £40 for the hack to lectures/the pub and then get something better for the weekend fun rides.

The only issue with this is that there are too many hipsters buying up old frames so the prices are rising.

Universities really should be doing more to provide safe cycle storage, the one I work at goes on about having "bait bikes" and police on campus but this obviously isn't much of a deterent as there are random smashed up frames and wheel locked to stands all over the place and the university can't can't be convinced to provide adequate locked storage, even for the staff.

When I got my job at Birmingham uni, I got myself a 5 year old Marin Pine Mountain, 91/92.  I love that bike.  20 years of getting me to work and getting about.   Best £250 I ever spent, rims were shot though.

Practically. It's going to be kept in a bikeshed so maintenance might be difficult. You are going to want to leave it outside halls of residence, around the campus and presumably outside the pub.

It's going to get abused and or nicked.

Don't buy something you are going to get upset about losing.

Having said that, a crap bike can be fun even if that means riding it into a canal whilst pissed. Oh how I miss those carefree student days.

NOTE - Do not ride your bicycle into a canal, it is extremely dangerous and annoys the fish.

What you might want is something battered but quality second hand.  Something unobtrusive but nice.  And reserve a fair bit for locks, maybe a good chain lock.  You are never going to eliminate risk of theft, your bike just needs to be a little less appealing than the blokes next to yours, generally.   And the state of some of the locking I have seen, no wonder unis are a hotbed of bicycle theft.

You might want to think about security skewers too, and watch a few youtubes on how to lock the bike.

Decathlon's a good value option but if bike theft is a problem and you're leaving it outdoors (even with the frame, both wheels and the saddle locked) then perhaps an even cheaper model? The 500SE has had great reviews, for example.

You might also think about buying something secondhand, perhaps something that's cosmetically not very appealing but in functionally good condition.

And - with other cyclists - lobby your college for better bike parking!