I have a Timbuk2 messenger bag and it's pretty good.

May I throw another option into the pool: how about a tote?

At my school, most girls use totes. Totes are nice because they are more versatile than your standard Jansport. It's been my experience that you can comfortably fit 1-2 texts and many notebooks or your laptop in a tote, so you aren't sacrificing utility. Depending on the design, you could seamlessly move between your internship and school.

I have a nice Land's End tote that zips and has big pockets as well as a d-ring for your keys.

This one is from Target costs $8

This design is getting pretty popular. You can get one for about $10 and it folds up if you don't want it.

If you're geeky, I recommend the The Bag of Holding messenger bag. I've just gotten it and oh my god, it's amazing. It can hold more than you can possibly think -- and doesn't hurt at all.

Warning: I have weird tastes.

If you're looking for a backpack, go with a Chrome.

As far as messenger bag, I would go with one of the Halliburton brief cases if you can afford it. Nothing says professional like bulletproof.

I'm not sure exactly what you mean by book bag-- is that a backpack? (This might be a regional language difference.) I have a pretty good backpack I've had for 5 or 6 years now that I got from LL Bean-- I have beat the crap out of that bag over the years and you can't even tell.

A book bag can hold a larger load, and does a better job of distributing the load over a larger surface area causing less stress on the bones. Book bags are not necessarily unprofessional, but they do tend to put out a student feel. A messenger bag usually can't hold as much as a book bag, and unlike book bags they only have one strap that tends to rest against your collarbone, this puts a large amount of pressure on a very small surface area. Certain messenger bags look more professional than book bags, but at the end of the day book bags tend to be more comfortable, durable, and can hold more than a messenger bag.

Some suggestions from personal experience:

http://www.amazon.com/Wenger-SwissGear-IBEX/dp/B000VSFLCI/ref=sr_1_5?ie=UTF8&s=electronics&qid=1261982535&sr=1-5 Pros: SwissGear IBEX gets me through a lot really durable back pack. I love it so much I bought one for my brother. Cons: Pretty damn expensive.

http://www.amazon.com/SwissGear-Computer-Backpack-Black-Gray/dp/B0019M6GP6/ref=sr_1_32?ie=UTF8&s=electronics&qid=1261982674&sr=1-32 Pros: another SwissGear, pretty durable price is average got me through high school. Cons: the computer pocket left me wanting for more.

Brands that I personally have experience with or that come highly recommended.

• SwissGear
• Targus
• High Sierra

In short, messenger bags do seem more professional than book bags, but book bags can hold more and tend to be better for the body, and more comfortable. In my opinion.