I haven't really seen many rare birds, so I am afraid I cannot answer this one.
I did see a Hoopoe in France if they are rare!
**This is an update!** I saw a Ringed-Neck Parakeet in London today.
Sorry the image isn't good quality, becasue I accidently deleted my best one!
http://i256.photobucket.com/albums/hh182...CF1235.jpg
In the UK: Grey-tailed Tattler, Ruppell's Warbler, Oriental Pratincole, Black Lark, Long-billed Murrelet, Spectacled Warbler, Green Heron, Rose-breasted Grosbeak, Cedar Waxwing, Cream-coloured Courser etc etc etc.
Plus lots of semi-rarities. I've been birding for a long time!
Jamie: Hoopoes are quite common on the continent (including France!)
ok then. I didn't know that
Possible Rosaete Tern....
Never seen a kingfisher, and not surprisingly this may jump straight into my top three birds when seen.
I told you I was new to this games, and to be gentle with me. Is a brambling rare enough to be mentioned?
I guess the title says the rarest bird 'you' have seen so I guess it is this beautiful finch for me.
Not into rare birds, but I have seen a corncrake and did stop off to see a rarity on Anglesey once, but I can't remember what it was!
Seen a Montagu's Harrier (well a pair of them) and a Bittern, thats probably the rarest in the UK, im not really a birdwatcher though so they probably dont fare well against some mentioned above

Brambling is a Rare bird for me, only seen one once. Don't know how rare these are...seen an Osprey, Alpine swift, Red grouse (rare for my area) and Montagu's Harrier. Though, if my County recorder saw my attempts at the bird quiz, i think he would inclined to drop these sightings
Chris.
The rarest birds I have seen are, Great Northern Diver, Little Egret and Ruddy Shelduck. I suppose the Ruddy shelduck would be the rarest of those.
The rarest birds I have seen are, Great Northern Diver, Little Egret and Ruddy Shelduck. I suppose the Ruddy shelduck would be the rarest of those.
Yes, I have also seen a Little Egret. They are there every time I go to my local river, the Crouch in Essex. I didn't think that they were rare actually, but you probably know better! 
YES!!! 10:30 this morning, I saw my first Ring Necked Parakeet in London! YES!!!

:)

:)

Little Egrets are more common I believe down your way but up here in north east scotland they are not very often seen. I saw one at Montrose Basin last year.
Never seen a kingfisher, and not surprisingly this may jump straight into my top three birds when seen.
I told you I was new to this games, and to be gentle with me. Is a brambling rare enough to be mentioned?
I guess the title says the rarest bird 'you' have seen so I guess it is this beautiful finch for me.
Of course it is! I have never actually seen a Brambling, so it is rare to me!
Little Egrets are more common I believe down your way but up here in north east scotland they are not very often seen. I saw one at Montrose Basin last year.
Oh right ok then. We usually get them during the summer time, but the odd Egret can be seen in the winter months.