I doubt that everybody here has perfect pitch (I don't), but it's pretty easy to remember vocal lines once you sing them.
Maybe it's to do with muscle memory and your body is able to remember the amount of tension the vocal chords need to reproduce a certain note perfectly

So basically, post certain songs which make it very easy to remember certain notes due to the vocal line.

For example:
Over the Rainbow.
When he sings the first lyric, 'somewhere', he plays a very recognisable C.

I Will
The first sung notes are G#, which fall down to C#. I used this song because it's quite stately and has alot of drawn out notes, making it quite memorable. I noticed the whole piece is actually in C# Harmonic minor, and uses every note from that scale at some point in the piece.
Breakfast, Breakfast, it's great for us
We eat, we eat, we eat
That frozen meat
Oh boy, oh boy, oh boy, it can't be beat
Anytime michael jackson does his signature "hee hee" it's always an interval of a third, whether its major or minor depends on the key of course but that's how I learned to recognize the interval. The sound of a doorbell going ding dong is also always a third so that's another way to remember.
Uploaded some MP3's onto my profile, please check 'em out & let me know what you think! :3