Yup, the day of the massive ERP suite and a huge, built-out HRMS system is dead. In HR, we now back to the modularized applications, but this time around, we can effectively tie everything together on the back end and provide an integrated presentation space to all users.
With the incredible depth in HR modules these days, you almost HAVE TO buy a separate LMS, ATS/HMS, comp system, and Benefit Admin system (or outsource). About the last thing that is integrated is PR and core HR, but even that changes if you outsource PR. Assuming that you accept my premise that data integration is directly related to process efficiency, You have to find a way to bundle everything seamlessly. For example, in one of my previous discussions, compensation analysis (usually in HR or a CMS) should be integrated with position management (usually in HR) should be integrated with labor standards (usually in time & labor) which finally flows over to staffing.
Basically you can now buy all the “best in class” software apps and (given the right budget) tie all of them together so they feel like one app. Portal services provide access to disparate databases (usually with a single sign-on if the target apps allow it) and a single presentation that is based on the security profile. So if you are a salesperson, you see a CRM and perhaps all your employee self service stuff. If you are a manager, you see MSS and ESS, etc…
The obvious leader in the industry (IMO) is Plumtree. There are other vendors like SAP who provide the same functionality, and the integration between existing SAP modules should already be mostly built. Other lower level vendors like Kronos, Ceridian & ADP provide portals, but your chances of linking their MSS/ESS portal to your CRM and and SCM are dubious.
Below is a great high level description of what a portal should do.