The 200 club
Which players have made at least 200 appearances (in all competitions) for their MLS team? It's a small list of only 22 guys, who have been major players in the history of the league:
CHI-Armas, Brown, Marsch, Thornton
CLB-Clark, Cunningham, Maisonneuve, McBride
KC-Garcia, Klein, Preki, Zavagnin
LA-Cienfuegos, Hartman, Jones, Vanney
DC-Etcheverry, Moreno, Williams
This year, Armas, Garcia, Henderson, Pareja, and Zavagnin have joined the club. I believe the closest player to 200 is Ben Olsen, but they need to advance in the playoffs and Copa Sudamericana for him to have a shot at it.
Also this year, Cobi Jones became the first to get 300 appearances for his club, the Galaxy. A quick check says that it occured on June 5 vs the Metrostars.
The top 5 teams on this list (CHI-CLB-DC-KC-LA) are all in the top 6 alltime record-wise (at least entering this season). The only one that isn't is San Jose, who really have had two seperate eras in their short history. KC has as well, but SJ has been more willing to change up their roster from year to year.