LimSee3 - This is a freeware open source java SMIL2.0 Authoring Tool. - http://limsee3.gforge.inria.fr/public-site/
Adobe GoLive - Consists of a SMIL editor. - http://www.adobe.com/web/wireless/mms.html
Cool MMS - This is a fun, easy-to-use, multi-page, template based MMS composer for Series 60 mobile phones. - http://www.wirelesscentral.com.au/products.asp
Motorola Messaging Suite - A set of tools to create and test MMS and EMS messages for Motorola's MMS and EMS-enabled handsets. - http://motocoder.com/motorola/pcsHome.jsp?rNum=-310741094&node_name=Messaging_Suite
InterObject MMS Composer and Player - This is a MMS Composer and Player for Windows and embedded systems. - http://www.inobject.com/MMS_composer.html