What exactly are you looking for?
Chipping on Astartes Armor
Weathering vehicles & terrain
What effect are you going for Muddy,Rusty,Old,Winterize
I am top notch with Vehicles and Terrain
Check out the first few pages of My Merican Lancer thread in off-topic
I started that project painting 10 Leman Russes in a WW2 Winter Sherman theme which uses pretty much all of the above,except mudhttp://z15.invisionfree.com/The_Great_Crus...wtopic=5040&hl=
I am a huge fan of all AK Interactive products and MIG powders.
For Marines I add a few chips with a fine brush and add a highlight underneath the chip.
Then I have rust drip from the chip.
Always remember less is more,too many/big chips and it looks like camo