Weddingbee boards

Well, first off just keep in mind that you don't have to do anything to keep your guests entertained. Really, providing a place to mingle, dancing, and some food is the basis for most weddings, and people have been having fun that way for centuries!

That said, if you want some additional ideas, I love creative stuff like this, so here's my master list!

Inexpensive (Or at least potentially inexpensive if you're crafty!)

Creative guest book. I won't go into the many possibilities here, but do a quick Google search, and you'll find dozens! Do a polaroid guestbook (that particular one is a bit pricier,) or have guests write a message on a keepsake (a canvas, edges of a photo of you, etc.)

Wish tree - again, you'd have to Google the specifics of creating one, but basically a place for guests to write messages to you that they hang on the wish tree

Fun facts about the couple - you can do this on the cocktail napkins, or at place settings

Photo display of the couple, or maybe a generational photo display of wedding pictures in your family

Fun favors - one 'silly' piece at an otherwise elegant wedding can really work - glow sticks, silly glasses, etc.

Couple games - make little crosswords or word searches that are couple themed

Lawn games if it's partially outdoors - croquette, horseshoes, etc. 

Moderate Expense

Buffets - candy buffets, cookie buffets, popcorn buffets, etc. People love mulling over what to put in their favor box!

Interactive food stations - a hot cocoa station with toppings, a s'mores station (yes, people do them now, so fun!) etc.

Photobooths and faux-to booths

Self-serve cigar bar outside for the men 

Caricature artist or silhouette artist to make artwork of the guests to take home

Live musician - guitarist, mariachi band, steel drum band, etc. 

Over the Top!

Live entertainment - dancers (belly dancers, troupes, etc.), magicians, contortionists, etc.

Cigar roller

Artist to create an oil painting of the wedding as it takes place

Fireworks