hi Linda some great advise here, I think the best advise has come from rick in regards to lens compatibility with full frame sensors, I am going down that exact route right now I also have the 600d and have just ordered a FF body most my lens are EF except for the recently bought 15-85 mm EFS lens, which is a great lens for landscape and general walk about, but I cant use it on my new camera so I will loose a couple of hundred dollars on that lens when I sell it. so if you think you'll be going down the FF path buy a EF lens now for your 600d. IMHO