In what season are you getting married? Below is a year of ideas to help you in your planning:

Winter
Holidays: Christmas & New Year's Eve
Popular Colors: Blue, maroon, dark, rich colors

Centerpiece Ideas:
Large snow globes
Pinecone or evergreen wreath with pillar candle inside
Ice sculptures
Decorated Christmas tree
Favor Ideas:

Miniature snow globes
Christmas ornaments
Evergreen-scented candles
Stuffed Christmas stocking

Spring
Holidays: Easter & Memorial Day
Popular Colors: Yellows, pinks & pastels

Centerpiece Ideas:
Tulips in watering cans
Small birdhouses
Small potted plants
Decorated Easter or May Day baskets
Favor ideas:

Small watering cans with a votive candles inside
Personalized seed packets
Flower bulbs
Chocolate Easter bunnies

Summer
Holidays: Fourth of July
Popular Colors: Sea green, peach, vibrant colors