There are so many flowers and herbs that are used as traditional wedding bouquets, but I really like the idea of choosing flowers for their symbolic meaning as well. Here's a few that I'm familiar with:
ferns: (commonly used as bouquet filler) denotes sincerity
globe amaranth: (small, round flower heads, can be found in shades of red, cream) denotes unfading love/eternal love
ivy: (nice for trailing bouquets and garlands for church decorations) represents fidelity
mint: (very aromatic and good for filling out a bouquet with greenery, some variegated varieties) also denotes love and passion
rose: many colors and varieties, this flower is most commonly representation of love (cabbage roses/flowering kale also looks gorgeous in fall and winter bouquets and has the same meaning)
sweet marjoram: (airy, small white-cream flower clusters that can be used in place of baby's breath) used in wedding garlands dating back to Greek times, considered "the herb of love"
oregano: (similar to sweet marjoram, ornamental varieties flowers vary from lavender to maroon), traditionally the Greek "herb of happiness"
rosemary: (good filler for winter bouquets, has both pine scent and appearance, but opt for non-flowering unless you like blue) - traditional "herb of remembrance and friendship", also traditional symbol of married love
Any combination of these can be used to create bouquets, garlands and table settings for a wedding. Another added benefit to many of these is that they dry nicely and can be kept as dried keepsakes from the ceremony.
To create a posy, go to the floral shop and ask for "nosegay holders". As you build the posy, start with your center piece (say, a rose or cabbage rose). Use a vase while working on your posy. Working in a circle, fill in with smaller flowers (sweet marjoram, globe amaranth), and build outward, finishing with ferns, mints or ivy. You can finish the base by running the gathered stems through a piece of lace and placing the ends in the nosegay holder. You can also wrap the holder with coordinating ribbons or bows to finish the bouquet.
Hope this gives you some ideas for selecting your wedding flowers.