Free massages! Sound sleazy? Don't worry - there are two reputable places in Sinnoh to get quality free massages for your Pokemon.
Veilstone City - Girl in southwest house
The girl here give a massage once per day to the Pokemon of your choice, which will slightly raise its happiness. She'll also randomly give you a Contest item for use in the Super Contests. Here's the list of possible items you can get here:
Resort Area - Ribbon Syndicate (2nd floor)
Those contest items you received from the lady in Veilstone will come in handy to get into this place - you need at least ten different kinds of Ribbons on any of your Pokemon to enter the Ribbon Syndicate in the Resort Area.
Go to the second floor to claim your free massage daily. You won't get any cool contest items out of it, but the massages here give a bigger boost to your Pokemon's happiness.