Any swimmers? Need workout ideas

I started swimming a few months ago, and currently manage approximately 1000m (mostly a time restriction, I have endurance, but should get faster, as on average I cannot stay at the pool more than 35-40 minutes at a time, and 1000m is about what I can manage before I have to leave. ).
I did follow some workouts for beginners these last months and they definitely worked, as I have doubled the distance I can cover. But I would hope to (1) increase speed and (2) add some variety.
Any ideas where I could get sample workouts?