Glitch - Mid-air Body Hop
This sometimes works, and only in certain conditions. Pick up any random flat item -- although dead bodies sometimes work -- jump into the air with the object in hand.

At the azimuth of the jump, toss the object downwards and sometimes your character will stop as if he stood on the ground (but in the middle of the air); if you jump again, your guy will start a jump from that spot in the air. It might prove helpful for some higher areas when your jump isn't high enough yet (due to lack of agility orbs or leveling).

Wall-Climbing SUV

First, obtain 4 stars in your Driving skill. In the Agency Garage, select the Agency SUV and head out to any building or wall with a flat surface. If its a building, make sure there are no ledges obstructing your path up the wall.

Next, get the SUV perpendicular to the wall you are going to drive up. Naturally, you must have your front bumper facing the wall/building.

After that, punch the gas. Your SUV's front tires should start creeping up the wall. Once they are firmly grasping the surface of the wall and your rear tires are about to do the same press down and hold the RED button to use your 4 star vehicle's special ability.

This ability pulls down your SUV's suspension, essentially hugging the wall you're riding up. Do not let go of the RED button unless you want to launch yourself off the wall.

Congratulations, if you have followed each step listed above you're now a wall climbing beast.

Now, if you hold the RED button down long enough while driving the 4 star Agency SUV you will notice the sound it makes. You can only hold the suspension down for so long before the effect times out and returns the SUV to normal. Take note of the sound your SUV makes as the suspension effect times out.

By taking advantage of this while driving up walls you will be amazed with the heights you can reach in this vehicle. Practice while you're driving on the ground so you can get the timing down. If you are hopping your SUV you are pressing the RED button again too soon.

This skill isn't ver practical but mastering it will let you can roar your beastly SUV straight up Wang Tower ... bypassing his elite guards.

Weapons List

A list of weapons, if you want to collect them all (like Pokemon but lethal):

Firearms
Agency Pistol (Colby 'Master')
Agency Assault Rifle (Colby EAR50)
Automatic Sniper (Bastion S600 'Long Eye')
Heavy Calibre Sniper (Bastion SX900 'Longshot')
Standard Pistol (Kokov 'Diktat')
Punisher Pistol (Smithers 'Punisher')
Standard SMG (Ingalls X80)
Short SMG (Harman MP-50)
M-60 (Ingalls MG-60)
Heavy Machine Gun (Harlington HMG-90)
Auto Shotgun (Dempsey 190 'Equalizer')
Store Clerk Shotgun (Dempsey SO-6 'Stub')
Grenadier (Watson HE79 'Grenadier')
Firefly Rocket Launcher (Watson HE99-X 'Firefly')
Hothead Rocket Launcher (Watson HE99 'Hothead')

Thrown Weapons
Remote Mines (Colby 'Limpet Charge')
Standard Grenade (Grenade)
Shrapnel Grenade (Shrapnel Grenade)
Cluster Grenade (Insta-death)