Here’s what i’ve found out. But I think the main area that you guys should hang out at sounds like Beyoglu.
MOJO is a rock bar with a good band named Circus on Saturday nights.Its known to be too crowded on fridays and saturdays though.

Across the street from MOJO is HAYAL KAHVESI, highly recommended rock bar.

MIKLA is a Turkish-Scandinavian fusion restaurant on the top of marmara pera hotel.

Here’s a good website to about Istanbul’s nightlife

http://www.i-gunler.com/en/istanbul_night.php

then there’s a new nightclub for musiclovers with art school students’ works hanging off the walls called GHETTO the address is Kalyoncuk Kulluk Avenue No: 10 Taksim

babylon is also very recommended, find the details on their website http://www.babylon-ist.com/b2003/en/index.asp

close to babylon is a restaurant called TAVANARASI which means “attic”. They have good food.

there are some winehouses across the British Embassy called PANO and VICTOR LEVI are good ones.

CEZAYIR is a good restaurant. find more details at http://www.cezayir-istanbul.com/en.index.htm

Link below is for the classical experience of turkish drinking, raki of course and mezes, a very mediterranean way of enjoying food and company. For a listing of “meyhanes” check below
http://www.mymerhaba.com/en/main/content.asp_Q_id_E_920

Check Peyote in Taksim as well, where awesome bands play.

enjoy! :)