We do a weekly garden bird count for the BTO* (also record stag beetles via the same site) I don't know what our annual total is but our weekly total is between 16 and 20 species. Our oddest over the years have been an escaped African Grey parrot and a small flock of (presumabley escaped) zebra finches one year. Ring necked parakeets (escapeees from the 1950s**) are now common in the area.

RtS
*British Trust for Ornithology
** allegedly escaped from a Shepperton film set. Possible Sanders of the River or similar.