I recently had been ask how persons usually not involved in Debian's development process can help Debian. This is a question that pops up quite often, so I thought I should write down a bit of that.
Help to make Debian a better OS
If you are using Debian, and you want something of your OS changed, open a bug report. This varies from wishlist bugs if you want to have an enhancement of a package over normal bugs for stuff that you think is a real bug up to serious or grave bug, if you found a security bug. Send a mail to firstname.lastname@example.org or use the tool reportbug and describe the problem you have found. Find more information here. Be as verbose as possible when explaining your problem. This will make it easier for the package maintainer to help you and to understand the problem. If you are not sure which package to report the bug against, report it against unknown. The bug will be taken care of, there are guys redirecting those bug reports to the appropriate package!
You could also help to verify bug reports. There are dozens of packages around, that have hundred of open bug reports. It will help the Debian package maintainer if you can tell him a "me too", esp for complex problems, or if you found out how to reproduce a bug.
Help by spreading the word
If you are using Debian, speak about it! If you have problems with Debian, speak about it! If you like Debian, speak about it. Read the debian-user mailing list (or a localized one) and jump in if users have the same problem you had, and help them.
All sort of publicity will help Debian. If there is a small exhibition near to your living, speak there about Debian, and how you are using it. Speak also to Debian, we can help you to announce your presence at that exhibition and provide you with information material in various languages. Good contact point for that is email@example.com, or one of the debian-events-* mailing lists on lists.debian.org. If you need help, ask for it. Also, you can help Debian manning an exhibition. If you see events in your area, offer to help and don't be shy. Other way to help is working with the publicity team and prepare press announcements, the Debian Project News (DPN), contact journalists or press media if interesting things happen in Debian.
Help Debian to organize stuff
There are many ways to help Debian organize itself. For example the annual Debian Conference DebConf is a big organisation monster, and you don't need to be developer to help with that. Sometimes it's as easy as helping in the video team taping the conference, help at the front desk with registration, sorting badges or speaking to the caterer about needed foods. We also have miniDebConf or so called Debian Bug Squashing parties from time to time. Your company could provide office rooms, you could provide crash space for developers to sleep or even by sponsoring some beverages or food. Also helping around exhibition is a good idea. If your company is willing to print some flyers or posters this can help us.
Help by translating or writing documentation
Debian's website and all of the software Debian delivers should be available in all languages around the world! Good starting point for that is http://www.debian.org/international/ and the Debian Internationalization Mailing list. Also writing or extending documentation is a job everyone can do. If you are using a piece of software heavily and miss documentation, speak to the Debian package maintainer (you can find our at http://packages.debian.org/$yourpackage) and start submitting bugs with documentation.
Help by donating
There are actually many ways to help by donating (not only by money). Surely Debian will accept money donations via one of it's official representation (ffis, SPI, debian.ch, ...). On the other hand donating can be as simple as allowing your employees to work some specified time on the week on Debian! Or you donate machine hardware (probably not your old ones that you used five years and which are not under warranty now any more, sorry...), bandwith or colocation in your datacenter. Speak to the hardware donations team if you want to know the current needs.
I only wrote down a very few areas where you can help Debian, and there are plenty more! Don't hesitate to jump in to help. If you don't understand stuff: ask! But be prepared that you will be pointed to URLs where the stuff you ask for is documented. Helping Debian sometimes starts with reading tons of documentation (and i am sure you will find errors in that documentation to fix!), but after a while it makes a lot of fun to work for and with Debian. Find your own area to work on within Debian, and don't think you can't help. Even graphic designers, lawyers or clerks can help Debian!
I started using Debian around 15 years ago and became Debian Developer around 6 years ago. Within the last six years I had been in various positions inside Debian (listmaster team member, volatile team member, release team member and Stable Release Manager, Debian Sysadmin Team member) and got to those just by jumping in where help needed.