Readomator in Lion works amazingly if you take a few minutes to download the high quality voices that are available from within your System Preferences.

Follow these steps to download free higher quality voices on OS X 10.7 Lion:

Open "System Preferences".

Select "Speech".

Choose "Customize…" from the "System Voice" popup.

For American English, check "Samantha" and "Tom". These are the two high quality American English voices available in Lion.

(Voices are also available in other languages and accents including Australian English, British English, Indian English, Irish English, Scottish English, and South African English. Select a voice and click play to test its quality for yourself.)

Click "OK".

Software Update will launch. Click "Install".

The selected voices will download. Voice files are very big. This may take a few minutes.

Once the selected voices have finished downloading, they will be available in Readomator and other text-to-speech apps.