The answer: lighting is a definite MUST and will give you an amazing bang for your buck. Do not leave it out of your budget if you want to create the perfect atmosphere for your wedding.
I haven't given much wedding advice so far, mostly because there is so much information out there already. However, something that is often overlooked when planning a wedding is the importance of lighting. People focus on venue, flowers, linens but tend to ignore lighting, other than perhaps one of those stencils on the dance floor. (My lighting designer was ECSTATIC when he heard that I absolutely did not want a "C & D" monogram projected for my wedding. Apologies to readers who incorporated that particular effect.) Lighting creates the mood for the event, makes it memorable, and can have a far greater impact than flowers.
So what did I do? Amber uplighting on all of the columns in the room. A "cool" lighting scheme in the bar, with a patterned gobo (bubbles). A "warm" lighting scheme on the walls - more amber, with a very organic, blurred gobo. An even "warmer," rose lighting scheme on the dance floor with yet another gobo - this one was the most distinct pattern and was a bit of a combination of the two.
If that means nothing to you . . . take a look. Lighting by Jon Retsky of Got Light in SF. Here's a link to all of the lighting photos from the night.