To add to this - keep things simple elegant instead of flashy. Flashy is expensive and actually does the opposite makes the wedding look cheap.
For example for table settings we used hurricane lamps that were supplied free of charge by our venue and to dress them up, we had simple greenery rings that went around the lamps rather than more expensive table bouquets.
Invitations were more simple and elegant rather than these flashy type pictures on them.
I agree with the flowers in season - they last longer, look fresher and cost less.
If you can hire a really good DJ - you get the bonus of having any sort of music or songs you want. A really good DJ is better than a poor band that is limited and costs much less.
A big cost saver is to have cash bar (and some venues depending which state you are located in recommend this for legality reasons - you could be liable for every guest if you buy their drinks) - what we did was provided x number of bottles of wine on each table with dinner. Guests could purchase other drinks if they wanted at a bar. Limited our liability and provided (what I felt) is appropriate drinking for a wedding.
If you want to provide open bar, I suggest limited to beer and wine. Consider having your venue at an estate or other venue you can rent. There are some beautiful places that you can have weddings where you bring in your own catering and bar service - that can lower prices of food/drinks as well.
One area I suggest not cutting on if the photographer - you can't get those pictures back if they do a horrible job.