One of the joys of Ultimate Frisbee
is the number of ad-hoc pickup games
that pop up just about anywhere ultimate is played. These games have a pleasant tendency to practically organize themselves
If you are in the Boston, MA area, be sure to check out Esplanade Ultimate, on the banks of the Charles River. We've been playing almost every Saturday since April 4, 1998 (including all Winter long). During the summer of 1999 we grew to over 200 members on the mailing list. In spring, 2002 we have over 500 members. A typical Saturday in mid-summer has two games of 7 on a side, with subs. Occasionally we start a third field if the numbers and interest is there.
The only time games are cancelled is if rain makes the field too soft and vulnerable to damage. For the latest, tune in to http://www.ihuck.com/eu and join the mailing list. There's a FAQ too. Getting to the field by T is easy. By car is possible, but one of the hardest things you may ever do in your life or the life of your car. Read Reverse Curve and related Boston driving links to get the flavor. The acutal directions are on the the IHuck web site.
What about other pickup games? The UPA (Ultimate Players Association, http://www.upa.org/) maintains a list of well-known games, but this list is not always up to date for a number of reasons.
Many urban games operate by the word-of-mouth principle, in which case the Internet (or even E2!) can't help much. Other games are publicized via various privately maintained mailing lists, the general rule for which is, if you are industrious enough to discover the list on your own, and write a happy letter to the list owner, they will usually invite you to swing by sometime and join in.
And of course there's you can always bike around on weekends looking for games. Ask before joining, but you usually won't be turned down if its just a pickup. If you find a game with people in (mostly) identical T-shirts, or all in skirts (cross dressing is still popular in some circles), it might be a league or an official team practice, so don't be disappointed. Ask them to direct you to other pickup games.
Oh yeah, and one other thing: GET HO!