My favorite is:

1/2 lemon
inch or two of ginger root
1/2 cucumber
6 stalks of kale
fill up to 16 oz with apple

Apple and carrot make great "filler" juices, meaning you can add **** tons of them and they won't overpower the flavoring of the juice.  Things like lemons, kale, ginger, beets are a bit stronger and I use less of them.  Some are in the middle like orange, cucumber, and pear.