Many thanks to each of you who replied.  It's always encouraging
to those of us who are still learning when you more-experienced
birders are eager to help us hone our skills.  A couple of you also
wanted to know what the consensus was.

Species suggest were Eastern Bluebird and White-eyed Vireo, though in
most cases with some uncertainty.  The Bluebird has a similar
two-note call (e.g. http://www.learnbirdsongs.com/birdsong.php?id=21
at 20 secs, thanks Phil).  To my ear, the one I recorded sounds 
qualitatively similar to the white-eyed vireo (e.g.
http://www.mbr-pwrc.usgs.gov/id/framlst/Song/h6310so.mp3 ,
though I compared it to my Peterson's CD).

Anyone caring to share thoughts between the two, I'd love to know
off-line.

Thanks again to those who responded,
Ryan Farrell
College Park

Here is the recording once again for anyone who missed it the first time:

http://www.farrellfam.com/Unknown30Mar07.WMA