I bet mom keeps my food under the sink
— Anonymous toddler

Best

Munchkin Xtra Guard Multi-Use Latch

$7.23

versatile and effective

You affix these adhesive mount locks to the front of cabinet doors. They also can be used on almost anything else (fridge, microwave, toilet, etc).  Installation takes just seconds and everyday use is fairly frustration-free.  The only real drawback is that they are visible on the outside of the cabinet, so if you prefer to keep your locks hidden, these might not be for you. 

Pros
Easy to install; Simple to use; Can be used anywhere

Cons
Visible on outside of cabinets


Better

Safety Baby Magnetic Cabinet Locks

$19.90 $39.99

Cleverly HIdden and Easily Trusted

These ingenious locks have a magnetic "key" that is used to open the cabinets.  Installation is a snap; just adhere the locks to the inside of the cabinet with the 3M adhesive specifically designed to withstand the yank of a toddler.  Place the key on the front of the cabinet to unlock it; there is even a setting to keep the cabinet unlocked for times when you don't want to always require the key.  We love how the locks remain concealed and they are super easy to use.

Pros
Concealed on inside of cabinets, Easy to install (no drilling needed)

Cons
Somewhat inconvenient to always use the key


Good

KisCords Cord Cabinet Lock

$9.95 $12.99

Works Well on Cabinets with Knobs

While not as versatile as the options above, if you have cabinets with side-by-side round knobs, these cord locks work really well and are easy to use.  The cords tighten around the knobs to prevent the cabinets from opening.  To open the cabinets, just slide the locking mechanism down and remove the cord from one of the knobs.   

Pros
Very easy to use

Cons
Limited to only cabinets with side-by-side round knobs