Microblogs are here to stay and the most important thing about microblogs is their immediate feedback information loop capabilities.

Some microblogs worldwide

This list is a personal choice and based on three criteria: ease of operability, quality of service and experienced functional up-time.

general
http://twitter.com
http://jaiku.com
http://pownce.com
http://yelago.com
http://beemood.com
http://yonkly.com


Chinese
http://fanfou.com
http://zuosa.com
http://komoo.cn

Indian
http://snockles.com

Singaporean
http://tiish.com

Italian
http://meemi.com

Spanish
http://khaces.com
http://fritsi.com

Turkish
http://nolyo.com

French
http://noumba.net
http://tapioka.ca
http://frazr.com

Korean
http://playtalk.net
http://me2day.net

Japanese
http://feecle.jp
http://haru.fm

German
http://niimo.com
http://dukudu.de

Polish
http://blip.pl

Dutch
http://numpa.nl

Portuguese
http://gozub.com

Russian
http://smspr.ru

Arabic
http://watwet.com

Romanian
http://cirip.ro

Mexican
http://mexicodiario.com

special
http://tumblr.com
http://hictu.com
http://babl.nl
http://floort.com
http://help.com
http://justtell.us

multiple posting

http://hellotxt.com


The most exhaustive list I know about is the list made up by thw http://www.thws.cn/articles/twitter-clones.html

Pieter Jansegers

http://microblogs.ning.com

I wrote 

also  Microblogs are changing the world

and  Why twitter is such a great success…