The Yards parking lots across First Street are a good option and are not listed on the Nats page 'cause they're operated privately. Go to http://www.networkparking.net/theyardsbaseball/index.shtml for information.
They're cheaper ($15-$25) than comparable Nats lots and they allow some tailgating (but no grilling.)
You get reduced rates (by $5) if you buy 20 or more passes. Best thing is that you don't have to buy for a whole season. That's ideal for ticket groups who have some members who want parking and some who don't.
Thanks for a great tip, got my passes today.
