Which bass should i buy?!?!???

I play alternative

Range price is $500-600

bands i like:
muse, radiohead, alter bridge, coheed and cambria, tool, dream theater

ESP!!! I have an LTD b304 and its excellent, you should definetely give the 400 series a spin.
Well, a Fender MIM P or J bass will do you good for pretty much anything. The Ibanez SR500 and SR600 are also very good and extremely versatile. The ATK series is quite good too. You could get a Spector Legend Classic, which is an awesome bass. I personally like the G&L JB-2 (but that might just be my G&L fanboy-ism there). ESP/LTD's are nice, and Schecter's can be great, but some people seem to just not like the feel of them, so I'd recommend trying it out. The Sterling series by Musicman makes a bass for $600 thats a budget version of a Stingray.

Basically, theres a ****load of options, your best bet is to try out as many basses as you can
Composite Aficionado

Spector and Markbass
I would probably go for a MIM fender
Ibanez RG4EXQM1
Fender Jazz V
Yahama Pacifica 112
Acoustic B200h
2 custom 1x15 cabs
Vox AD30VT
too many pedals
My band take alot of influence from most of those bands, I like to use a Traben Chaos Obsession, the sound of it seems to just work well along side the rest of the band. Although, it is pretty hard to go wrong with Fender. It might also we worth looking into a used Warwick, or one of the new line of Warwick Rockbasses.