Vicki - I travel to London a couple times a year and never run out of things to see and do but one of my favorites is the Tower of London, a trip through Harrods to see all the beautiful things, especially the food hall, an evening at the theater, (you should be able to find out what's playing on line) a visit to Buckingham Palace and also the mews (where they keep all the gorgeous antigue carriages) that way you can see the changing of the guard. Have fun
If you are into shopping, you'll want to visit Piccadilly Circus and, of course, Harrod's.
Also, be sure to get over to Westminster to see the gardens in front of Buckingham Palace. From there, it's an easy walk to the Westminster shopping district -- and be sure to visit Westminster Cathedral, which is hidden behind a row of stores, but easily accessible, in the shopping district. Continuing toward the Thames, you can see Westminster Palace (where the English Parliament sits), Westminster Abbey, and Big Ben.
If you are more into sightseeing, you might want to consider a day in the country. Stonehenge, Bath, Cambridge, and Oxford are all easy day trips from London.
We (husband, wife, son 17 & son 13) just got back from London and highly recommend the double decker bus tour ( makes frequent stops where you can get off and on all day) which stops by most of the tourist places, Buckingham Palace (changing of the guard happens at 11:30 every morning during the summer), Harrods, and defininely see some plays. We saw "We will Rock You", which was the best. It contains 32 songs by Queen. Another great play is "the Complete Works of William Shakespeare (abridged)" by the Reduced Shakespeare Company. It consists of 3 Americans preforming 37 Shakespeare plays in 97 minutes. Great fun. On Tuesday's the same company does "500 years of American History in 6000 Seconds". Not as good as Shakespear, but a good laugh. Remember, there are same day, half off theater ticket booths but the availability changes daily. So if there's a play you really want to see and it's fairly new, you're better off gong on line and purchasing the tickets before you arrive. If you're a family, we recommend you get a family "all day" pass for the Tube (underground). It cost us about 9 pounds total for the day, but since you only have 2 day, we highly recommend the bus tour. Wear some good walking shoes and enjoy.
Thank-you for your help. We are really getting excited as our time gets closer. We will defiently do the bus tour the first day and must see the British Library, changing of the guard and have tickets to Ceremoney of the Keys at the Tower of London.
Thanks again for all the good advice.