Unlock Any Mission:
The following cheats will allow you to unlock any mission of your choosing in the mission select screen. Bring down the console with the tilde key (button to the left of "1") in game and type the following commands to unlock your desired mission sets.
Unlock "Hill 400" Mission Set /seta mis_09 9
Unlock "The Battle For Caen" Mission Set /seta mis_08 9
Unlock "D-Day" Mission Set /seta mis_07 9
Unlock "Rommel's Last Stand" Mission Set /seta mis_06 9
Unlock "The Tank Squadrons" Mission Set /seta mis_05 9
Unlock "Fortress Stalingrad" Mission Set /seta mis_04 9
Unlock "Not One Step Backwards!" Mission Set /seta mis_03 9
Unlock "The Battle Of El Alamein" Mission Set /seta mis_02 9
Unlock "The Winter War" Mission Set /seta mis_01 9
Unlock "Crossing The Rhine" Mission Set /seta mis_10 9

Play Any Mission:
Bring down the console in game with your tilde key (the key to the left of "1") and enter the following to play your desired mission. This will allow you to play missions you are yet to unlock.
Play "The Crossing Point" map rhine
Play "Stalingrad City Hall" map cityhall
Play "Comrade Sniper" map downtown_sniper
Play "Crusader Charge" map libya
Play "88 Ridge" map 88ridge
Play "Armoured Car Escape" map toujane_ride
Play "Retaking Toujane" map toujane
Play "Assault On Matmata" map matmata
Play "The Battle Of Pointe Du Hoc" map duhoc_assault
Play "Defending The Pointe" map duhoc_defend
Play "The Silo" map silotown
Play "Prisoners Of War" map beltot
Play "The Crossroads" map crossroads
Play "The Battle For Hill 400" map hill400_defend
Play "Rangers Lead The Way" map hill400_assault
Play "Bergstein" map bergstein
Play "The Brigade Box" map breakout
Play "The Tiger" map newvillers
Play "Downtown Assault" map downtown_assault
Play "Railroad Station No. 1" map trainyard
Play "Repairing The Wire" map tankhunt
Play "The End Of The Beginning" map eldaba
Play "El Alamein" map elalamein
Play "Holding The Line" map decoytown
Play "The Diversionary Raid" map decoytrenches
Play "Demolition" map demolition
Play "Red Army Training" map moscow

Demo Cheats:
At the main menu screen of the demo enter the "Game Options" and Enable the Console. From there, push your tilde (~) button to bring down the console and type the following:

seta thereisacow "1337"
followed by
spdevmap eldaba

This will start the demo level with devmap and cheats enabled. This allows you to use any of the commands in game without restriction. When in game, bring down the console and enter any of the commands from below to activate the 'cheat'.
Walk / Fly through walls. noclip
Each time it's entered you'll be given 2 different weapons from the demo. give all
Infinite health. god
Enemies ignore you. notarget
Refill your ammunition / grenades. give ammo
Moon jump (jump_height 39 for default). jump_height 128
Slow motion (timescale 1 for default). timescale .25