I bought a Columbia waterproof jacket a couple years back and have noticed this year that it isn't very waterproof anymore.  What do you guys use to re-waterproof them?

You might try a silacon spray they use for tents.

You can try a dry cleaners. My wife used to work at one and they did waterproofing of jackets, tents, boat tops, etc.

Falcon

"water resistant" is the word you meant

This means the outer layer is "treated" but it is not "forever".  3m Scotchguard is basically what they use.

"water resistant" is the word you meant

This means the outer layer is "treated" but it is not "forever". 3m Scotchguard is basically what they use.

Just reading what it says  

I'll have to check the dry cleaners.  Thanks