Valve has added bots to TF2. They are available using the following commands:

Originally Posted by Valve

# To add bots to your game, use the console command tf_bot_add. This will drop a random bot onto a random team (assuming there is a free player slot). The tf_bot_add command can also take up to three optional arguments: <count>, <class>, and <team>, in any order. For example, tf_bot_add 10 will add 10 random bots to the game with auto-assigned teams. Typing tf_bot_add pyro blue will add a Pyro to the blue team. Entering tf_bot_add red 5 will add 5 random bots to the red team. The command tf_bot_add red 3 heavyweapons will add three heavies to the red team.

# In order to put specific bots on specific teams (for a bots-vs-humans game, for example), you may want to disable automatic team balancing. To do this, enter mp_autoteambalance 0 followed by mp_teams_unbalance_limit 0.

# To remove a bot, use the console command kick <bot name>. To remove all of the bots in the game, use the command tf_bot_kick all.

I 'm not a big fan of bots but it might be an interesting feature to help seed servers.