I enjoyed the TV series The Great British Dig where Hugh Dennis presents a team of archaeologists digging in peoples gardens. Here's what I have found in mine so far, not much of a coin hoard unfortunately. First a 1967 halfpenny.
More valuable (at the time!) a 1949 George VI florin (2 shillings old money, 10p today). They removed all the silver from the coinage in 1947 so this one hasn't survived very well. The nickel plating has mainly gone showing the copper base.
As our house is the first dwelling erected on this site as far as we can tell (late 60's) I wasn't expecting much but 2/- and a ha'penny was a little underwhelming. Anything more exciting turned up during your garden excavations?