Thanks, rhema! Very interesting!!
OpenSecrets.org has chronicled the top 100 political givers from 1989-2008. The top 16 appear below, the two teacher unions being #7 and 16. After the group's name and cumulative dollars donated, the first percentage is donations to Democrats, the second percentage to Republicans.
1 American Fedn of State, County & Municipal Employees $39,392,153 98% 1%
2 AT&T Inc $39,065,076 43% 56%
3 National Assn of Realtors $32,336,506 47% 52%
4 American Assn for Justice $28,727,389 90% 9%
5 Goldman Sachs $28,701,957 62% 36%
6 Intl Brotherhood of Electrical Workers $27,898,934 97% 2%
7 National Education Assn $27,713,779 93% 6%
8 Laborers Union $26,503,339 91% 7%
9 Service Employees International Union $25,931,093 95% 3%
10 Carpenters & Joiners Union $25,627,582 89% 9%
11 Teamsters Union $24,992,064 92% 7%
12 Communications Workers of America $24,871,179 99% 0%
13 American Medical Assn $24,728,871 38% 61%
14 United Auto Workers $24,343,620 98% 0%
15 Citigroup Inc $24,271,821 49% 50%
16 American Federation of Teachers $24,113,243 98% 0%
If you're keeping score at home, that's $49,887,057 to Democrats, $1,662,827 to Republicans.