Here's the list of supported and non-supported countries: 
http://www.google.com/support/androidmarke...?&answer=138294

For those in the country that are currently not supported, here's a work around (this works on my Eee Pad Transformer  )
1) Go to Settings -> Accounts & Sync -> Manage Account and select your Gmail account, then click <remove account>
2) Go to Settings -> Applications -> Manage Applications -> All
Select every single Google App (Google Accounts, Google Backup Transport, ...) and click <Clear data> for each of it

This gets rid of all location information 

3) Power off and then power on the device.
4) Click on the Market icon, it will request you to key in your gmail account
5) use the same gmail account but use @googlemail.com instead of @gmail.com
6) the apps that are not allowed to be installed in the device's country will have the file size of 0.00B (that's ok!)
7) click on the <download> button**

There are some apps that are not compatible with the ASUS Eee Pad Transformer/Android 3.x Honeycomb (eg. DME mail client). 
** The apps that are not compatible will not download. The above steps are only for the apps that have the error message "cannot be installed in the device's country".

Repeat the above the next time you encounter that error message! Good luck.
[Thanks to Ms. Siti of Asus Customer Care Centre, Malaysia!]

If (5) above doesn't work... ask your friend in one of the supported countries to forward your new GMail account's verification sms to you 

The Eee Pad Transformer is amazing especially with the Tegra optimized games!!! 
www nvidia com/object/tegra-zone.html

BR//Timothy

1) Download and use anycut to create shortcut to hidden proxy setting
2) Get a us based ip port proxy from hidemyass or just google it
3) Set proxy setting to any proxy you pick
4) Remove your account from pad/tablet from account & sync in settings
5) Run android market, re-enter your account
6) I think you can remove the proxy after this as it is no longer required (after the next update or whenever android market cache is cleared)

Slightly more detailed:

Note 1: You need to just add the proxy IP address and Port. Leave the rest blank.
Note 2: One site where you can get a list of Proxy IP is: www.hidemyass.com.
Note 3: You need to try and try until you find a proxy that is good -- fast and reliable.