I'm also curious as to what Mass Effect races the Borg might take an interest in...
Advanced technology, hardy biology... Yeah, they'd be a nice addition to the collective.
Most Quarian tech is scavenged from here and there, and the Quarians themselves have piss-poor immune systems. The Borg would regard them in the same way as the Kazon, I reckon.
With their homeworld bombed back to the stone age, the Krogan don't have much technology to offer. However, they are a long-lived race and can heal rather rapidly, so they would probably make excellent drones.
I know the Geth are entirely mechanical, but so is Data and the Borg tried to convert him in First Contact. Mind you, Locutus said in Best Of Both Worlds that Data would be obsolete when the Borg conquered Earth, but I see no real reason why the Borg would disregard androids and robotics when they assimilate all other manner of advanced technology.
Not sure. They're very intelligent and have an extremely analytical way of thinking, but their lifespans are shorter than most other species. They do have some great tech, though.
Technologically advanced, long-lived, excellent genetics and their entire race is biotic. Oh, the Borg would love these ladies!
I have no idea. I'm not sure how advanced they are or if they're biologically significant enough to arouse the Borg's interest.
They may not be humanoid, but why should the Borg only care about bipeds? They'd make terrific ground troops for future planetary invasions.
The Reapers and the Borg have so much in common. They're both cybernetic, both uber-powerful and commit destruction and murder on an unquantifiable scale!
Of course, they'd probably (definitely) try to kill each other... >_> REAPERS VS. BORG! TAKING ALL BETS!!