Here are the demo servers. Good luck.
Type /connect serverip to join them. Although like Drum said, the game is dirt cheap now and a lot better than the demo.
^4_><_^7Slow Rail-Freeze TDM | 66.55.154.45:27960
SS| 1V1 RAIL | 69.93.43.234:27959
#1 Clan 1vs1 Rail | 65.25.61.70:27960
*W*A*S*T*E*Fun*Freeze | 67.19.212.99:27961
Evolution's 1v1 | 67.19.212.99:27963
Tenacious D Time | 67.19.17.54:27961
Flash's (2) Freeze*Rail* | 67.19.212.99:27964
.o2o. freez-ffa | 67.19.212.101:27960
Flash's Freeze*Rail* | 67.19.212.99:27960
*TEXAS*HELL*FREEZE* | 67.19.212.100:27900
*W*A*S*T*E*Rail*Freeze | 67.19.212.99:27962
CTF Demo Style | 67.19.17.54:27962
Clan #1 Freeze.Rail | 67.19.212.98:27964
Mongolian Championship Tournament | 67.19.17.54:27964
Team Tenacious D Time | 67.19.17.54:27963
SDSL+FastEthernet+Death=Trouble | 67.19.17.54:27960
Linux Quad Arena | 24.160.238.74:30000
oNu (2) Rail Freeze TDM | 216.254.115.200:27961
*TK*TEXAS*1V1 | 24.0.106.73:27960
{KC}Bring*it's Freeze | 24.0.194.1:27960
POS | 141.158.41.98:27960
San Diego 1vs1 Server | 207.158.23.135:27961
Demon UK Q3 Demo (1) | 217.172.182.41:27960
xXx - <Triple X Server> | 217.172.182.41:27980
Demon UK Q3 Demo (2) | 217.172.182.41:27970
>>> R@IL PRO <<< | 195.13.62.107:28200
>>> R@IL PRO 2 <<< | 195.13.62.107:29000
Q3 Demo FFA DM7 | 219.38.60.120:27961