I am currently working on a project which requires migration of content from different content management Systems to SharePoint. Are there any good, preferably open source, tools that would help me do this? Also, what are the best practices that I would have to keep in mind when it comes to such projects. One more thing that i would like to factor here is reusablity, because we might have to work on similar migration projects, from other Content Management systems in future.
You can check http://www.codeplex.com/SPMigration (open source, project started by a Microsoft consultant).
This framework gives you an importer tool, as well as some exporter example (FileSystem for example). You'll problably have to code your own exporter.
This MSDN blog also goes into some detail about the Migration API and may be useful as its generally very had to do this sort of thing without getting your hands dirty
Also, IMHO you shouldn't dismiss proprietary products as although they can be expensive they may save you considerable time and therefore cost if you have a large conversion project.
http://www.tzunami.com/Pages/default.aspx
http://www.avepoint.com/products/sharepoint-migration
Tricks and tips - http://www.parallelspace.net/portals/ALS305-mwherman-Content%20Migration-1-1-18-RC6_FINAL.ppt
We have had good mileage from going to the nearest university and grabbing some IT students to do a manual migration.
The students like the extra cash and it is sometimes easier when the Information Architectures of the site changes between systems.