I was just reading weather's thread on him reaching 200 on his life list, which is a coincidence, as I wanted to reach 250 this year on my UK Life List and have managed to do it !! 
I started the year on 221, which wasn't bad considering I only 'twitched' one bird last year and that was the Sora at Attingborough NR. So I had some work to do this year, but I hit my goal of 250 earlier this month !! (I have now gone passed 250!!).
I honestly cannot remember my 200th species of bird, but I think it was possibly Sooty Shearwater?... I dont know, I'm certain it was a seabird of some description though.
But my 250th was a little cracker .... Rustic Bunting at Spurn this year!! Arriving to discover that the bird had 'flown' and then 10 minutes later to find it AND get brilliant views was very rewarding.
Out of my 250 though, I think that Bearded Tit comes in as my favourite and possibly hardest worked for too, dipping them at Titchwell and then managing to see them at Radipole was great !!
I now have the big climb up to 300 .... this is going to be hard, I think! 