This site has good information about the various radios on the 737 classic vs. NG, which will be similar to other modern airliners (though locations may differ somewhat). The graphics at the bottom show the external antennas, which include (for the NG):

1. Glide Slope - for ILS guidance
2. Localizer - for ILS guidance
3. Weather Radar
4. GPS
5. Radio Altimeter
6. ADF 1 - Navigation
7. ADF 2
8. Marker Beacon - for approach guidance
9. DME - Navigation
10. VOR - Navigation
11. TCAS x2
12. ATC 1 - probably transponder
13. ATC 2
14. VHF 1 - Regular voice communication
15. VHF 2
16. HF - For long range voice communication, such as oceanic crossings
17. ELT - Emergency Locator Transmittor

Please note that the above location diagrams are only a guide as the antenna fitted depends upon the customer avionics options. Eg some NG's do not have ADF but do have SATCOM or IFTS/Airphone.

More and more planes have satellite antennas for in-flight internet access, too. Military planes will also include more antennas for things like UHF and SATCOM.

Another site offers some details about certain radios on the 737 NG, including the power each one uses:

HF Voice Transceiver        400W
VHF Voice Transceiver       25W
DME (962 to 1150 MHz Xmit)  316W
Radar Altimeter (4300 MHz)  400mW
TCAS                        400W
Transponder (1090 MHz)      631W
WX Radar (9.3 Ghz)          120W 

For instance, it's interesting how the HF radio uses much more power than the VHF radio, and that the transponder uses the most power on the list.

This site has good information about the various radios on the 737 classic vs. NG, which will be similar to other modern airliners (though locations may differ somewhat). The graphics at the bottom show the external antennas, which include (for the NG):

1. Glide Slope - for ILS guidance
2. Localizer - for ILS guidance
3. Weather Radar
4. GPS
5. Radio Altimeter
6. ADF 1 - Navigation
7. ADF 2
8. Marker Beacon - for approach guidance
9. DME - Navigation
10. VOR - Navigation
11. TCAS x2
12. ATC 1 - Maybe transponder, ACARS
13. ATC 2
14. VHF 1 - Regular voice communication
15. VHF 2
16. HF - For long range voice communication, such as oceanic crossings
17. ELT - Emergency Locator Transmittor

Please note that the above location diagrams are only a guide as the antenna fitted depends upon the customer avionics options. Eg some NG's do not have ADF but do have SATCOM or IFTS/Airphone.

More and more planes have satellite antennas for in-flight internet access, too. Military planes will also include more antennas for things like UHF and SATCOM.

Another site offers some details about certain radios on the 737 NG, including the power each one uses:

HF Voice Transceiver        400W
VHF Voice Transceiver       25W
DME (962 to 1150 MHz Xmit)  316W
Radar Altimeter (4300 MHz)  400mW
TCAS                        400W
Transponder (1090 MHz)      631W
WX Radar (9.3 Ghz)          120W 

For instance, it's interesting how the HF radio uses much more power than the VHF radio, and that the transponder uses the most power on the list.