TTS Builder Pro allows engineers to create their own Text To Speech Voice or Language using High Quality Open Festival Speech Synthesis Research. A complete step-by-step manual for such a creation is included in the retail version. The evaluation version has one such British Voice created using the mentioned step-by-step techniques. The TTSBuilder converts the heavy technical research oriented documentation into one simple practical guide, all you require to do is follow the steps. Not to mention all required libraries for Windows are included. This is an Research Lab attempt to bring speech synthesis to basic developers.

Festival Speech Synthesis Research allows one to create production level Text To Speech Engines
Tools
Available : A complete multi-lingual speech synthesis workbench off research
Ported to Embedded : Edinburgh Speech Tools Library
Open DSP Library : libsnd.dll
CMUdict -- pronunciation dictionary
Ported
OpenVXI -- VoiceXML browser
SALT browser -- finally online!
Audio Databases -- AN4, Microphone array, etc
Advised TTS for Dictionary Resource:

The DICT Development Group: Clients for the RFC 2229 dictionary protocol.
Encyclopedia Britannica: Just like the twenty-book set, but it fits in your web browser.
Hypertext Webster Gateway: Search engine spanning multiple dictionaries.
IEEE Keywords: List of approved IEEE keywords for indexing publications.
Merriam-Webster Online: Perhaps the best on-line dictionary available.
Roget's Thesaurus: The all-in-one desktop reference - search the web, a dictionary, and Roget's Thesaurus.

Directories possible
555-1212: look up a telephone area code.
AnyWho: look up any address by it's telephone number.
CEOExpress: highly informational site catering to business professionals.
MapQuest: get directions anywhere in the US.
United States Postal Service: look up a zip code.

General Databases
CMU ARCTIC, 4 single speaker speech databases with around 1200 phonetically balanced utterances.
CMU FAF, 107 paragraphs (15,000 words) of single speaker monologues with interesting prosody. Basic of Aesop's fables and country descriptions in the CIA world fact book.
CMU SIN, speech in noise: speech recorded while noise is playing in the speakers ears (and when not).
CSTR US KED timit University of Edinburgh's male US TIMIT, 452 phonetically balanced utterances.
Limited Domain Databases
Telling the time
The current weather (in US)
Communicator dialog
Diphone Databases
CMU US KAL diphone
CSTR UK RAB diphone
MBROLA voices and binaries
Check out these MBROLA projects wide range of pre-built diphone databases for many languages and binaries for the mbrola program itself for many platforms.

The license of this software is Free Trial Software, the price is $199, you can free download and get a free trial.