The Niles Audio DBI-2 was the most popular solution in home automation systems, but it was discontinued about a year ago. Below are replacements I've seen recommended on various forums, in addition to the Gilderfluke mentioned above:

[Link: barix.com]
[Link: frightideas.com]
[Link: alcorn.com]
[Link: technovision.com]
[Link: bcsideas.com]
[Link: vikingelectronics.com]
[Link: vikingelectronics.com]
[Link: bogen-paging.com]
[Link: rdlnet.com]

The only one I've personally used is the Barix, which is great, and can do a lot more than simply playing sound files.