Here is a graphic lists out Green cards issued between 2003 and 2005. Mexico leads the table followed by India and China in that order. The report has lots of interesting statistics that might interest you. I understand each country has some kind of quota allocated for Green cards. If these statistics speak for any thing, then India got around 7.5% allocations in the quota.
In 2005, a total of 1,122,373 persons became LPRs ofÂ the United States (see Table 1). The majority (66 percent) lived in the United States when they became LPRs. Nearly three-fifths (58 percent) were granted permanent residence based on a family relationship with a U.S. citizen or legal permanent resident of the United States. The leading countries of birth of LPRs were Mexico (14 percent), India (8 percent), and China (6 percent).
Reference : Annual Flow Report April 2006
Tags: Greencard, immigration, india, mexico