One of the things that bugs us all about Google is how to contact them about new features, bugs, help, downtime, etc. I've complied a quick list of services/products they offer and the links you need to contact Google about the service. Also, I've included links for the Google Group and Help center related to that specific service/product.

Google Help A – Z: http://www.google.com/support/bin/static.py?page=alpha_index.html

Adsense
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Contact Us: https://www.google.com/adsense/support/bin/request.py
Google Group: http://groups.google.com/group/adsense-help?sourceid=asos&subid=ww-en-et-homepage&medium=link
Help Center: https://www.google.com/adsense/support/

Adwords
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Contact Us: http://adwords.google.com/support/bin/request.py?ctx=cuffanswer
Google Group: http://groups.google.com/group/adwords-help/
Help Center: http://adwords.google.com/support/

Base
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Contact Us: http://base.google.com/support/bin/request.py
Google Group: http://groups.google.com/group/base-help-discussion
Help Center: http://base.google.com/support/

Blog Search
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Help Center: http://www.google.com/help/about_blogsearch.html#support
Email Support: blogsearch-supportgoogle.com

Books
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Email Support: books-supportgoogle.com
Help Center: http://books.google.com/support/

Calendar
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Contact Us: http://www.google.com/support/calendar/bin/request.py
Google Group: http://groups.google.com/group/Google-Calendar-Help/
Help Center: http://www.google.com/support/calendar/

Checkout (Buyer Help)
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Contact Us: https://checkout.google.com/support/bin/request.py
Help Center: https://checkout.google.com/support/

Checkout (Seller Help)
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Contact Us: http://checkout.google.com/support/sell/bin/request.py
Help Center: http://checkout.google.com/support/sell/?hl=en

Earth
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Contact Us: http://earth.google.com/support/bin/request.py
Google Group: http://groups.google.com/group/earth-help
Help Center: http://earth.google.com/support/

Gmail
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Suggest a Feature: http://mail.google.com/support/bin/request.py?contact_type=suggest
Contact Us form: http://mail.google.com/support/bin/request.py
Google Group: http://groups.google.com/group/Gmail-Help-Discussion
Help Center: http://mail.google.com/support/

Google.com Search
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Contact Us: http://www.google.com/support/bin/request.py
(Same form is used for Images.google.com)
Help Center: http://www.google.com/support/

Google Groups
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Contact Us: http://groups.google.com/support/bin/request.py
Google Group Help: http://groups.google.com/group/Google-Groups-Guide
Help Center: http://groups.google.com/support/

Maps
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Contact Us: http://maps.google.com/support/bin/request.py
Google Group: http://groups.google.com/group/Google-Maps
Help Center: http://maps.google.com/support/

News
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Contact Us: http://news.google.com/support/news/bin/request.py
Google Group: http://groups.google.com/group/googlenews-help
Help Center: http://www.google.com/support/news/

Scholar
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Add your website for inclusion: http://www.google.com/support/scholar/bin/request.py
Help Center: http://scholar.google.com/intl/en/scholar/help.html

Toolbar (Firefox)
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Contact Us: http://www.google.com/support/firefox/bin/request.py
Google Group: http://groups.google.com/group/FFToolbar-Group
Help Center: http://www.google.com/support/firefox/

Toolbar (Internet Explorer)
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Contact Us: http://www.google.com/support/toolbar/bin/request.py
Google Group: http://groups.google.com/group/IEToolbar-Group
Help Center: http://www.google.com/support/toolbar/?hl=en

Video
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Contact Us: http://video.google.com/support/bin/request.py
Google Group: http://groups.google.com/group/Google-Video-Help
Help Center: http://video.google.com/support/

Just a note, Please don't abuse the contact us forms before you take the time to find a solution in the help center and/or Google Group related to the product/service your inquiring about.

Nice list, that permalink will be used quite often to send others to.

All these are available using a simple google search and the links are available in the help center of each google service. But that doesn't mean they're useful and someone Google actually answers your question.

http://www.google.com/search?q=gmail+contact
http://www.google.com/search?q=add+site+to+google+scholar
http://www.google.com/search?q=google+maps+group

Not all of the Contact Us links was easy to find by going to help center of the specific product. Thats why I originally created the list so I wouldn't have to hunt for it.