Searching for iPhone 4S, iPhone 4, iPhone 3GS, iPhone 3G, iPhone 2G firmware restore .ipsw links? Below is a list of direct links for every firmware released.

Note: Updates will be posted as the latest firmware versions are released (latest version iOS 5).

1.0.0: iPhone1,1_1.0_1A543a_Restore.ipsw
1.0.1: iPhone1,1_1.0.1_1C25_Restore.ipsw
1.0.2: iPhone1,1_1.0.2_1C28_Restore.ipsw
1.1.1: iPhone1,1_1.1.1_3A109a_Restore.ipsw
1.1.2: iPhone1,1_1.1.2_3B48b_Restore.ipsw
1.1.3: iPhone1,1_1.1.3_4A93_Restore.ipsw
1.1.4: iPhone1,1_1.1.4_4A102_Restore.ipsw
2.0.0 (2G): iPhone1,1_2.0_5A347_Restore.ipsw
2.0.0 (3G): iPhone1,2_2.0_5A347_Restore.ipsw
2.0.1 (2G): iPhone1,1_2.0.1_5B108_Restore.ipsw
2.0.1 (3G): iPhone1,2_2.0.1_5B108_Restore.ipsw
2.0.2 (2G): iPhone1,1_2.0.2_5C1_Restore.ipsw
2.0.2 (3G): iPhone1,2_2.0.2_5C1_Restore.ipsw
2.1.0 (2G): iPhone1,1_2.1_5F136_Restore.ipsw
2.1.0 (3G): iPhone1,2_2.1_5F136_Restore.ipsw
2.2.0 (2G): iPhone1,1_2.2_5G77_Restore.ipsw
2.2.0 (3G): iPhone1,2_2.2_5G77_Restore.ipsw
2.2.1 (2G): iPhone1,1_2.2.1_5H1_Restore.ipsw
2.2.1 (3G): iPhone1,2_2.2.1_5H11_Restore.ipsw
3.0.0 (2G): iPhone1,1_3.0_7A341_Restore.ipsw
3.0.0 (3G): iPhone1,2_3.0_7A341_Restore.ipsw
3.0.0 (3GS): iPhone2,1_3.0_7A341_Restore.ipsw
3.0.1 (2G): iPhone1,1_3.0.1_7A400_Restore.ipsw
3.0.1 (3G): iPhone1,2_3.0.1_7A400_Restore.ipsw
3.0.1 (3GS): iPhone2,1_3.0.1_7A400_Restore.ipsw
3.1.0 (2G): iPhone1,1_3.1_7C144_Restore.ipsw
3.1.0 (3G): iPhone1,2_3.1_7C144_Restore.ipsw
3.1.0 (3GS): iPhone2,1_3.1_7C144_Restore.ipsw
3.1.2 (2G): iPhone1,1_3.1.2_7D11_Restore.ipsw
3.1.2 (3G): iPhone1,2_3.1.2_7D11_Restore.ipsw
3.1.2 (3GS): iPhone2,1_3.1.2_7D11_Restore.ipsw
3.1.3 (2G): iPhone1,1_3.1.3_7E18_Restore.ipsw
3.1.3 (3G): iPhone1,2_3.1.3_7E18_Restore.ipsw
3.1.3 (3GS): iPhone2,1_3.1.3_7E18_Restore.ipsw
4.0.0 (3G): iPhone1,2_4.0_8A293_Restore.ipsw
4.0.0 (3GS): iPhone2,1_4.0_8A293_Restore.ipsw
4.0.0 (4): iPhone3,1_4.0_8A293_Restore.ipsw
4.0.1 (3G): iPhone1,2_4.0.1_8A306_Restore.ipsw
4.0.1 (3GS): iPhone2,1_4.0.1_8A306_Restore.ipsw
4.0.1 (4): iPhone3,1_4.0.1_8A306_Restore.ipsw
4.0.2 (3G): iPhone1,2_4.0.2_8A400_Restore.ipsw
4.0.2 (3GS): iPhone2,1_4.0.2_8A400_Restore.ipsw
4.0.2 (4): iPhone3,1_4.0.2_8A400_Restore.ipsw
4.1.0 (3G): iPhone1,2_4.1_8B117_Restore.ipsw
4.1.0 (3GS): iPhone2,1_4.1_8B117_Restore.ipsw
4.1.0 (4): iPhone3,1_4.1_8B117_Restore.ipsw
4.2.1 (3G): iPhone1,2_4.2.1_8C148_Restore.ipsw
4.2.1 (3GS): iPhone2,1_4.2.1_8C148a_Restore.ipsw
4.2.1 (4): iPhone3,1_4.2.1_8C148_Restore.ipsw
4.2.6 (4 CDMA): iPhone3,3_4.2.6_8E200_Restore.ipsw
4.3.0 (3GS): iPhone2,1_4.3_8F190_Restore.ipsw
4.3.0 (4 GSM): iPhone3,1_4.3_8F190_Restore.ipsw
4.3.1 (3GS): iPhone2,1_4.3.1_8G4_Restore.ipsw
4.3.1 (4 GSM): iPhone3,1_4.3.1_8G4_Restore.ipsw
4.3.2 (3GS): iPhone2,1_4.3.2_8H7_Restore.ipsw
4.3.2 (4 GSM): iPhone3,1_4.3.2_8H7_Restore.ipsw
4.2.7 (4 CDMA): iPhone3,3_4.2.7_8E303_Restore.ipsw
4.2.8 (4 CDMA): iPhone3,3_4.2.8_8E401_Restore.ipsw
4.3.3 (3GS): iPhone2,1_4.3.3_8J2_Restore.ipsw
4.3.3 (4 GSM): iPhone3,1_4.3.3_8J2_Restore.ipsw
4.2.9 (4 CDMA): iPhone3,3_4.2.9_8E501_Restore.ipsw
4.3.4 (3GS): iPhone2,1_4.3.4_8K2_Restore.ipsw
4.3.4 (4 GSM): iPhone3,1_4.3.4_8K2_Restore.ipsw
4.2.10 (4 CDMA): iPhone3,3_4.2.10_8E600_Restore.ipsw
4.3.5 (3GS): iPhone2,1_4.3.5_8L1_Restore.ipsw
4.3.5 (4 GSM): iPhone3,1_4.3.5_8L1_Restore.ipsw
5.0 (3GS): iPhone2,1_5.0_9A334_Restore.ipsw
5.0 (4 GSM): iPhone3,1_5.0_9A334_Restore.ipsw
5.0 (4 CDMA): iPhone3,3_5.0_9A334_Restore.ipsw
5.0 (4S): iPhone4,1_5.0_9A334_Restore.ipsw
5.0.1 (3GS): iPhone2,1_5.0.1_9A405_Restore.ipsw
5.0.1 (4 GSM): iPhone3,1_5.0.1_9A405_Restore.ipsw
5.0.1 (4 CDMA): iPhone3,3_5.0.1_9A405_Restore.ipsw
5.0.1 (4S): iPhone4,1_5.0.1_9A405_Restore.ipsw

Check out Where To Download iPad Firmware Restore Links, Where To Download iPod Touch Firmware Restore Links, and iJailbreak Downloads Section.