The forthcoming marriage of Wills and Kate provides the chance for some to celebrate, others to complain, and for royal memorabilia collectors to make profitable investments.

Collectibles associated with Royal romance can command huge sums at auction, which should come as no surprise when one considers that two billion people are expected to watch the event on Friday.

Royal jewellery is a particularly strong area among collectors.

There is currently much debate as to whether Kate Middleton will borrow the Queen's "George III" tiara, which was made in 1919 and worn by the Queen Mother, the Queen and Princess Anne at their weddings. One tiara that she won't be wearing is the Poltimore specimen, sported by Princess Margaret on her wedding day in 1960. It made £926,400 at Christie's in 2006.

Wallis Simpson's jewellery achieved £31m at Sotheby's in 1987, including a Mclean diamond ring which made £1.8m. Edward VIII famously abdicated the throne in 1936 so he could marry the twice divorced Wallis.

Many Commonwealth countries are producing commemorative postage stamps for the occasion. Sadly for collectors, they are generally produced in such numbers that they are of little investment value.

However, the Pacific island of Niue has provoked comment through the release of an unusual pair of stamps that can be split down the middle, separating the happy couple in the process. Produced by New Zealand Post, these items could well interest those with an eye for the unusual.

Kate Middleton’s dress sold for £78,000, earlier this year

Dresses are also hugely popular with investors. A replica of Lady Diana's 1981 wedding dress, made for a Madame Tussauds waxwork , auctioned for £100,000 in 2005. And Kate Middleton's famous fashion-show item was recently purchased for £78,000 - which also sparked considerable press interest.

Of course, not every marriage works out, especially if you're Henry VIII.

The King's 1529 letter to the Bishop of Ravenna, requesting an annulment of his marriage to Catherine of Aragon so he could wed Anne Boleyn, is currently available on the private market with an asking price of £275,000.

But what should the investor be on the lookout for this time around?

Well, nothing is too bizarre to make a profit. A slice of Charles and Diana's wedding cake realised £17,000 in 1998…