What are the most popular Cubs tickets?

In 2005, I looked at "What type of Chicago Cubs tickets sell out first" and made a few observations:
1) August sells out faster than September.
2) Saturday sells faster than Sunday.
3) "Sold out" doesn't always mean sold out

Here's some more observations to tack on from 2006:

4. White Sox, Cardinals, Astros?
The White Sox opponent tickets sell out first, and then the Cardinals. It's rather amusing that the Astros are the National League Champions, and they haven't sold out any tickets at Wrigley Field. Chicago should totally know that the Astros won the NL, cuz they played the White Sox in the World Series!

5. Night games don't sell out THAT fast
It's also interesting that of the 28 games that are sold out in one day, only two are night games--both against the Cardinals.

6. Top Rivals
Other than White Sox and Cardinals, what are the most popular rivals of the Cubs? Here's a list of the Saturday sellouts in order:
1. Cubs vs. White Sox 7/1/2006-Saturday 12:20pm
1. Cubs vs. Cardinals 7/29/2006-Saturday 3:05pm
2. Cubs vs. Cardinals 8/19/2006-Saturday 12:20pm
3. Cubs vs. Cardinals 4/8/2006-Saturday 1:20pm
3. Cubs vs. Tigers 6/17/2006-Saturday 3:05pm
3. Cubs vs. Mets 7/15/2006-Saturday 3:05pm
4. Cubs vs. Braves 5/27/2006-Saturday 12:20pm
6. Cubs vs. Pirates 8/5/2006-Saturday 3:05pm
6. Cubs vs. Giants 9/2/2006-Saturday 1:20pm
7. Cubs vs. Brewers 4/29/2006-Saturday 1:20pm
7. Cubs vs. Padres 5/13/2006-Saturday 1:20pm

I have a feeling that the Pirates are only in there, because it's an August game. The only Saturday game that has not sold yet is:
---Cubs vs. Rockies 9/30/2006-Saturday 3:05pm
Which seems odd to me, because it's the second to last game of the season, if any season records are to be broken, it could be that day. That also could be the day the Cubs clinch their division or a wild card spot.