Ok - firstly the bouquet does not need to be thrown, it can as Jen did, be presented to a special person (Mum, Nan, Sister, Maid/Matron of Honour).
Secondly in most cases, from my experience, the actual bridal bouquet is not thrown but a smaller "throwaway" bouquet is. This being the case, as mentioned, the bridal bouquet can be kept and preserved or placed on a loved ones final resting place.

Finally, in case you didn't know - here is how this tradition originated;
In medieval Europe, the bride did not typically expect to wear her wedding dress again and the dress was considered good luck by other women, a type of fertility charm. After the wedding, single women would chase the bride and tore pieces off her dress, leaving her in tatters (I can just imagine a exclusive designer wedding dress being ripped to shreds - lol). Over the years, wedding dresses became more expensive and it became traditional for women to keep them, either as a memento or to pass on to a daughter for her wedding day.
To prevent guests from ripping the wedding dress, brides began throwing other objects as a distraction, one of which was the garter. Later, the bouquet became the most traditionally thrown object. The wedding bouquet is particularly suited to this use, as flowers symbolise fertility, and as perishable items, they are not something the bride would normally wish to keep. The bouquet is also a safer item to toss than the garter, as unruly and impatient wedding guests were sometimes known to try to take the garter from the bride while she was still wearing it (imagine girls, all the guests trying to get the garter of your leg!). Of course the woman who catches the bouquet is said to be the next who will marry.
As mentioned above, not all modern brides and grooms like the tradition of throwing the bouquet and either modify it or do away with it altogether.