I'm volunteering my free after work time for the Prague Fringe Festival this year (same as I did last year).

http://www.praguefringe.com/2008/programme.php
From the insiders perspective of Fringe Festival:

I would recommend to see/hear at least:
-40 Feathered Winks (touchy feeling...)
-Adolf (mind opening... please remain till the very end of the story
even if you feel like quitting in the middle)
-Sax to the Max! (many many great musicians exported from UK in
location that is normally hidden from general public)
-Magic & More with Frisco Fred (just hilarious)


Personal rating:
1. Magic & More with Frisco Fred
18:30 - 19:30 Divadlo Na Prádle - Kavárna
Comedy On The Square
Come spend a fun hour with the world's only nearsighted comic, magician, ...

2. 40 Feathered Winks
21:00 - 22:00 Divadlo Na Prádle
The Paper Birds
One third of human life is spent in bed; resting, crying, hiding,
lovemaking, ...

3. Adolf
8:15 - 19:15 Nosticovo divadlo
Pip Utton
Utton, looking uncomfortably like the Fuhrer, stands before a huge Nazi ...

4. Karagiozis Exposed
19:30 - 20:20 Divadlo Na Prádle
Open Arts
Karagiozis is a Cypriot shadow puppet. Through a mistake of his
puppeteer, ... In English and French


I heard was good (did not verified yet myself):
-The Sacred Sow
19:30 - 20:30 A Studio Rubín
Prague Playhouse
Dark and lyrical, the play's characters spin yarns about themselves, each ...

-The Tale of a T-Shirt
18:30 - 19:30 Divadlo Inspirace
Kennwort:Bergstation & Fixt Point Theatre
Float around the world as you follow the fantasy of a t-shirt, from cotton ...

-A Stretch of the Imagination
19:45 - 20:45 Nosticovo divadlo
Monk and Mort
Monk O'Neil, in the back of beyond, is facing death alone, with resilience ...


For those who appreciates music and songs:
-Sax to the Max!
19:30 - 20:30 Kostel sv. Jana Křtitele na Prádle
The National Saxophone Choir of Great Britain
SAX to the MAX! pushes the energy and imagination of thirty feisty
saxophonists ...

-Yellow Sisters
5:30 - 16:30 Divadlo Na Prádle
Ženská vokální skupina (Female a cappella group)
"… four hearts, four souls, four voices, four ways to share emotions ...

Some photos from volunteering times here /some more here / from Kostya.