My department is looking for software that can be used to deliver
notifications to individuals via email, mobile devices or instant
messaging, based on specific profile and subscriptions the individual
defines.

The specific requirements include:
1) Delivery to multiple channels according to user's definition:
email, pager, mobile phone, IM
2) Subscription capability allowing individual users to define the
type of notifications desired (i.e. Industry News; Corp
Communications; Support Requests; etc)
3) Profile management - ability for an IT manager to centrally define
what different users are/can subscribe to.
4) Ability to connect to multiple sources of content and events - both
internal databases and applications as well as external sources - via
Web Services.
5) Can support at least 500 users concurrently

I would appreciate pointers to software vendors who provide such
solutions (peferably around 10 such vendors);
Any type of rating between these vendors as well as some pricing
indications.

Thanks