Yesterday I did a search on the internet to see if I could find a better
way to brush up on bird songs (and learn new ones) before spring migration
is in full swing than just listening to the compilations of bird songs that
I have on itunes and on my iphone, and was rather excited to find a site
called "Larkwire.com" which sells what seems to be a game based, match the
bird to the song in various challenging ways... The approach seems to be
progressive and increasingly challenging.. I've played it off and on for
two days, and it seemed impossible at first.. I jumped to the "Pro" level
package, though within that there are still beginner, intermediate,
advanced.. and Master, I think. I've jumped to intermediate, and thought it
does seem to be very challenging, I do think it is sharpening my ears a lot
already.  It does't give you just one version of a bird song, it throws in
lots of variation that you don't get exposed to just listening to tapes.

Here's the link if anyone wants to check it out http://www.larkwire.com/