Ah, the smell of erasers and chalk dust is in the air, which can mean only one thing: it’s back to school time in many parts of the world. While I’d be lying if I didn’t say I was happy my school days are behind me, I am a bit jealous that students heading back to school now have a plethora of great web and mobile applications to help them tackle the tasks involved with obtaining an education. I would have killed for some of the great applications available to students today — almost all of which are cooler (and more useful) than the Tetris app I used to play on my graphing calculator.

In this list we’ve assembled ten of the must-have iPhone applications for students heading back to school. These apps will help you stay organized, take notes, and study better. What other iPhone applications are helpful to you at school? Please add your favorites in the comments.

1. BigWords (FREE)

BigWords is a very handy iPhone application that lets users search the BigWords.com textbook price comparison search engine while on-the-go. That’s helpful for checking out whether you can get a better deal online while shopping for books at your college’s campus bookstore. Other textbook apps to check out are CourseSmart’s eTextbooks (Free), which lets users access over 7,000 digitized textbooks from the iPhone, and the Stanza (Free) eBook reader from Amazon-owned Lexcycle, on which users can access over 50,000 free books (including many classics taught in high schools and colleges).

2. iStudiez Pro ($2.99)

iStudiez Pro is a beautiful, if oddly spelled, application that keeps track of your entire class schedule and assignments. From detailed, color-coded class schedules (the color coding makes the whole thing very easy to scan) to the ability to attach assignments to each course that shows up on the calendar and when they’re due, iStudiez Pro is a must-have companion to busy students. Also check out My Schedule ($0.99), a slightly cheaper but less feature-filled alternative that allows students to make iCal-style, color-coded class schedules and attach notes to each class.

3. Evernote (Free)

If you plan at all on using your iPhone for taking notes in class, you’ll want to utilize Evernote (). The free application supports text, photo, and voice notes, and syncs to an online account, as well as Mac and PC versions of the app so you can have access to your notes anywhere. Evernote has some really nifty features, such as Twitter () integration, geo-location, and the ability to search text within photos.

4. SimpleMind (Free / $6.99)

SimpleMind is a very easy-to-use mind mapping tool for the iPhone. The free version lets you create and export Mind Maps in the SimpleMind format, and the pay version lets you export your mind maps in OMPL, Freemind, PDF, and PNG formats. Start with the free version to get the hang of it and make sure the app is for you, then upgrade or try iThoughts ($7.99) or iBlueSky ($9.99).

5. Cram ($6.99)

Got a big test coming up? You’ll want to check out Cram. Cram is a study tool on which users can create flash cards and multiple choice tests (with automatically randomized answers). These study aids can be shared with friends and synced to the offline Mac OS version. Also check out StudyBlue (Free), which links to a StudyBlue.com account to let users study visual flash cards and review uploaded documents (Word, PDF, PowerPoint, images, etc.).

6. Wikipedia (Free)

The free Wikipedia () application launched just last month, and provides on-the-go, mobile optimized access to Wikipedia articles. Though Wikipedia should probably not be used as a primary source in any academic paper, it is a great starting point for deeper research, and the Wikipedia iPhone app lets you search the encyclopedia whenever an idea strikes you. Also check out Wikipanion (Free / $4.99), which in many ways is cleaner and more fully developed than the official app.

7. Dictionary.com (Free)

Dictionary.com is an invaluable application for students to keep in their iPhone backpack. The app provides full mobile access to both Dictionary.com and Thesaurus.com, which makes it insanely useful both while reading difficult texts and writing papers.

8. myHomework (Free)

The free myHomework app is a visually stunning iPhone application that helps students stay organized by creating a calendar of assignments and when they’re due. Assignments are color coded, so you’ll know when due dates are coming and when they’re late. The app doesn’t do much more than that, but it is helpful for keeping overloaded students on top of their work. Also check out MyClasses ($1.99), which keeps track of assignments and grades, iHomework ($0.99), a to-do list aimed at students, and Assignments ($1.99).

9. PI83 Graphing Calculator ($0.99)

For those in need of a graphing calculator for school, a better deal can’t be found. The PI83 Graphing Calculator application faithfully recreates the feature-set of the Texas Instruments TI83 graphing calculator on the iPhone, and for 99 cents, it does so for a lot less dough. There are some bugs that need to be worked out, but it is still one of the best graphic calculator applications in the App Store ().

10. Facebook (Free)

After all the hard work, you need to unwind a little as well. And what better way than with Facebook’s () iPhone application? If you’re in school, there’s about a 99.99% chance you’re on Facebook already, and their iPhone application is one of the most popular of all time on that platform. It lets you connect to the social network’s best features while on-the-go and a new version should be arriving any day now.

More iPhone resources from Mashable:

- 14 iPhone Apps With Push Notification for Productivity
- 29 Twitter Apps for the iPhone Compared
- 7 iPhone Apps That Can Save Lives
- 15 iPhone Apps to Tame the Kids
- 10 Fantastic iPhone Apps That Use Facebook Connect

Image courtesy of iStockphoto (), eurobanks