I found an active testnet node here:
http://testnet.mojocoin.com/aboutYou can add it in a few ways:
In your bitcoin.conf file (requires software restart):
addnode=199.26.85.40
Directly into a running instance of bitcoin-qt through the debug console (no restart):
addnode=199.26.85.40
Directly into a running instance of bitcoin daemon (no restart):
bitcoind addnode=199.26.85.40
When starting bitcoin daemon:
bitcoind -addnode=199.26.85.40
Also, Bitcoin Abe for Testnet can be found here:
http://pool.qdoop.net:18331/chain/Testnet3