Well, perhaps it's an overstatement to say you can't live without them. But these are 10 modules I have found indespensible in the process of making web sites since Drupal 6 has launched.

#1 - CCK (content consturction kit)

This module allows you to add any number of fields to a node (piece of content). At first this may not sound extremely exciting, but once you realize the amazing power of this feature, you will never start setting up a Drupal site without it. Once added to the #2 choice, it becomes unbeatable.

#2 - Views

This module is essential to almost any site. It allows you to take basically any information out of your Drupal Database and display it however you want. A thousand examples wouldn't scratch the surface of what all this could mean once you add in CCK. With the two you can create a piece of content or a content type that represents any piece of data, then display them in lists and format those lists in any way you choose.

There are a number of plug in modules for the two above as well which extend different fields and different display types.

#3 - Pathauto

One of the great features of Drupal is it's ability to do clean URLs. This is great for people using your web site, and even better for Google to be able to index your site. The trouble is that Drupal on it's own doesn't always know the best way to display those URLs. Pathauto gives you the ability to make the URLs on your site display as anything you wish. You can add dates, titles, and all sorts of other information to the URLs to make them easy to read and good for search engines.

#4 - TinyMCE

My WYSIWYG (What you see is what you get) Editor of choice. TinyMCE comes with a load of features to allow users of your web site to format the text that they enter. While on the one hand I would prefer to enter HTML, this is not the case for most people. The module is a little finicky to get set up, but once it's going your users or client will thank you very much.

#5 - ImageField

This is one of those plugins for CCK mentioned above. It allows you to add Images to Content which can later be displayed in all sorts of different ways with Views. Images is one of those things that stumps everyone starting out with Views, and there are a number of ways to go about it. This is one of my two ways to tackle images.

#6 - IMCE

I mentioned two ways to tackle images and this is the second one. IMCE integrates with TinyMCE (again with a little bit of work) to allow images to be directly uploaded and placed inside the content with your WYSIWYG editor. This is great for blogging, or site administrators who need to put arbitrary amounts of pictures in various places on a page. If the requirements are more straight forward, like one image in the same place at all times or a list of images, then ImageField with CCK and Views is likely a better solution.

#7 - ImageCache

To complete my mentions of image related modules, this is another essential one. It works with Views and ImageField for displaying images. It allows various transformations of image sizes and filters before displaying images. This takes one of the burdens off of site administrators of always having to make sure the images are the same size, and makes it even possible to change the site layout as well without having to resize all of the images. It saves a copy (cached file) on the server's hard drive so that it can serve it up just as quickly as the original image and makes for a very friendly experience when using the site.

#8 - Backup and Migrate

Backup is essential in all things with computers. Your data is important so you need to back it up. This module gives a simple way in the user interface to back up your whole Drupal Database to the file system, which means when you back up all of your files then you have a completely restorable site if your server were to go down. Without the database, your site is useless and all your data is lost.

#9 - Google Analytics

Another essential thing is knowing what's going on with your site. Drupal has some basic statistics, but it's nothing compared to what Google Analytics gives you, and Analytics is completely free. This module allows easy integration.

#10 - Zen Theme

Actually, this isn't a module at all, it's a theme. However, I think it's one of the greatest contributions so it gets honorable mention here. Zen Theme is downright ugly to begin with, because it has no styling. It allows you to style your entire web site using only CSS (and some additional modifications if your layout strays too much from the original.) It adds lots of great features to your theme in order to make a totally custom theme much easier to set up. It's of course possible to use one of the other contributed themes as a starting point, but I've found this to truly be the best.

Well hopefully this helps to get some people on the right track with choosing some great modules. If you have some you can't live without that didn't make my list, then feel free to comment on your top modules here!