Press ~ during game play to display the console window. Then, type sv_cheats 1 to enable cheat mode:

Code ~.~ Result:

bot_add_ct or bot_add_t ~.~ Allow bot to join game for indicated team
impuse 101 ~.~ Ammunition for weapons
bot_auto_follow ~.~ Bot automatically follows you if you do not give them orders
bot_prefix <prefix> ~.~ Bots have a prefix in their name
bot_knives_only ~.~ Bots use only knives
bot_defer_to_human 1 ~.~ Bots will not do mission objectives and will expect humans to do it
bot_kick ~.~ Kick all bots from game and leaves humans to play
bot_kill ~.~ Kill all bots
bot_show_nav ~.~ See where bot is going
give <name> ~.~ Spawn indicated item
bot_stop <0 or 1> ~.~ Toggle bot AI
bot_pistols_only <0 or 1> ~.~ Toggle bot using pistols only
bot_snipers_only <0 or 1> ~.~ Toggle bot using snipers only
sv_clienttrace 99999999999 ~.~ Weapon hits nearest enemy

Weapon names - Use one of the following entries with the give code to spawn the indicated weapon.

In counter strike source, change what weapons bots have in the console:

bot_allow_<weapon> (0 or 1)

replace the <weapon> with the name of the category of weapon you wish to change. 0 turns it off and 1 turns it on:

M249 (heavy machine gun): weapon_m249
TMP (silenced SMG): weapon_tmp
M4A1 (silencable rifle): weapon_m4a1
Deagle (Night Hawk): weapon_deagle
HE grenade (high explosive): weapon_hegrenade
AWP (magnum sniper rifle): weapon_awp
P90 (gun with 50 bullets per clip): weapon_p90
Scout (weakest sniper rifle): weapon_scout
Glock (terrorist default pistol): weapon_glock
Sent in by: HeadShot King