Some python code I wrote over a weekend to compute tax rates for various brackets.
Do what you want, but don't sue me if it doesn't compute your tax properly. I'm 
not a CPA or tax consultant and the software comes with absolutely no warranties.

Here's what ./compute.py generates for me:

Income 	Tax    	Effective Rate
0010000	0000665	6.65
0020000	0001405	7.03
0030000	0003150	10.50
0040000	0005095	12.74
0050000	0007500	15.00
0060000	0009977	16.63
0070000	0012552	17.93
0080000	0015169	18.96
0090000	0017914	19.90
0100000	0021212	21.21
0125000	0029993	23.99
0150000	0038349	25.57
0175000	0046745	26.71
0200000	0055781	27.89
0225000	0064818	28.81
0250000	0073854	29.54
0275000	0083754	30.46
0300000	0093925	31.31
0325000	0104095	32.03
0350000	0114265	32.65
0375000	0124435	33.18
0400000	0134606	33.65
0425000	0144776	34.07
0450000	0155048	34.46
0475000	0165672	34.88
0500000	0176296	35.26
0600000	0219441	36.57
0700000	0263236	37.61
0800000	0307031	38.38
0900000	0350826	38.98
1000000	0394621	39.46
1100000	0439716	39.97
1200000	0484811	40.40
1300000	0529906	40.76
1400000	0575001	41.07
1500000	0620096	41.34
1600000	0665191	41.57
1700000	0710286	41.78
1800000	0755381	41.97
1900000	0800476	42.13
2000000	0845571	42.28
3000000	1296521	43.22
4000000	1747471	43.69
5000000	2198421	43.97
6000000	2649371	44.16
7000000	3100321	44.29
8000000	3551271	44.39
9000000	4002221	44.47