Narrator for Windows (all versions) has a few built-in options for male and female voices.

To set Narrator voice options (Microsoft)

Here is a good source for more voices:

Best Free Windows Narrator Voices You Can Use (Zero2000.com)

Excerpt:

In the world of today, more and more people use the text to speech computer technology to free their eyes and save time. As a vital component of the text to speech technology, voices, i.e. speech engines, are the core of text to speech software. Because text to speech software need to invoke voices to synthetic speech and output spoken audio.

There are many voices available on the Internet today, such as AT&T Natural Voices, Cepstral voices, IVONA voices, CereProc voices, NeoSpeech voices, etc.. But most of these voices are commercial and the prices are even higher than the prices of normal text-to-speech software. For example, the prices of AT&T Natural Voices are $35 (base required) plus $35 per additional voice, and the prices of Cepstral voices are &29.99 per voice.

Fortunately, there are also enough high-quality free voices we can use. Most of them are compatible with the Microsoft SAPI 4 or SAPI 5. Generally, the higher SAPI version, the better quality.

Here is the free voices list sorted by the recommended degree.

Microsoft Mike, Mary and Sam -

Microsoft Sam is the default English male voice shipped with Microsoft Windows 2000 and Windows XP. Though not the default, Microsoft Sam is also available in Windows Vista Home Premium. It is used by Narrator, the screen reader program built into the operating system.

Microsoft Mike and Microsoft Mary are optional male and female voices respectively with better quality, available for download from the Microsoft website or other third party text-to-speech related websites.

The most noticeable feature of these three voices is there are both SAPI 4 and SAPI 5 versions of them. SAPI 5 voices are only available on Windows 2000 and later Windows NT-based operating systems. As an exception, the SAPI 5 versions of these voices cannot be installed on Windows Vista and Windows 7. The SAPI 4 versions are more compatible. They can be installed and used on Windows 98 and all the later Windows operating systems.

Microsoft Anna -

Microsoft Anna is the default English voice shipped with Windows Vista and Windows 7. Microsoft Anna is a SAPI 5-only voice and is designed to sound more natural than the previous system default voice Microsoft Sam.

This excellent female voice is base on the new Microsoft SAPI 5.3/5.4. So you cannot use it on Windows XP directly and also there is no standalone installer of this voice on the Microsoft website. The only way to use this fantastic voice on Windows XP is by the Microsoft Streets & Trips. The Microsoft Streets & Trips 2006 and later versions install the voice and the new Microsoft SAPI onto Windows XP computers for the voice-prompt direction feature.

Some third party text-to-speech related websites supply smaller repacked Microsoft Anna installers for Windows XP users. However, it's incomplete and not working correctly on Windows XP because the SAPI version of Windows XP is 5.1.

Lernout & Hauspie Voices -

Lernout & Hauspie Speech Products, or L&H, was a leading Belgium-based speech recognition technology company. This company released dozens of high-quality SAPI 4 voices across multiple languages, including ten American English voices and two British English voices.

In addition, Lernout & Hauspie Michael and Michelle are also optional male and female voices licensed by Microsoft from Lernout & Hauspie, and available through Microsoft Office XP and Microsoft Office 2003 or Microsoft Reader.

Most of the above voices can be found on the Microsoft's website or downloaded directly from the 2nd Speech Center web site. Click here to download them immediately.