This morning I updated a couple of things on Basketball-Reference.com.
First, you can now select rows to sum on the player game logs. For example, go to Michael Jordan's 1986-87 Game Log. Suppose you want to see Jordan's statistics for his first five games that season. To do this, click on the row for his first game of the season (the row should now be highlighted in blue), then click on the row for his fifth game of the season. A pop-up will appear with Jordan's per game averages for those games.
Second, I added an option to the Player Game Finder that will allow you to search by the player's game number rather than just the team game number. For example, here are the highest scoring debuts of the last 10 seasons.