"previous" buffer?

[Lev Lvovsky]

In regards to moving around buffers, is there any way to move between  
the last two buffers that were worked on?  Meaning, if I have 10  
files in buffers, and I'm working on buffer 5, switch to buffer 8,  
how can I switch back to buffer 5 without knowing its number (but  
knowing it was the last buffer I was editing)?

thanks!
-lev