I will use this pictures from Seattleflowers.com to show you some of the possible shapes of a bouquet.
Personally I'm a big fan of hand-tied bouquet. I love the natural look of it. I find it very romantic, never over the top, perfect for a feminine but modern bride.
The only tip about the bouquet is to choose something that will enhance your dress instead of taking away from it. The bouquet should never be too big, for example, it should complete your outfit not cover it!!
Another bouquet that I really like is the over arm (see one by sophiesflorist.co.uk) here below.
The only problem could be that they tend to be a little heavy and could be uncomfortable o carry around for the whole day!