Seems like an odd question, but I'm seeing an incrase in the number of
sites out there that are posting seemingly legit mp3 files out there,
with little fear of legal action being taken against them. If you look
at this site (http://wirez.wxcs.com/audio.php) you'll see that this
guy has a couple of albums that he is hosting. My question is, are
thes files likely "spiked", in that these files have malware or
something piggybacked on them? Is this becoming a common trend for
these types of sites? If these do indeed carry trojans, will a typical
virus scan catch these trojans? What should I be aware of before
downloading these files, outside of spyware/malware?

I cant speak for this site but most sites which allow these downloads
are illegal.  I personally use one site in which members rip and post
music to share with eachother.  No its not legal...

The most common example of a mp3 file being infected is when it
actually is not an mp3 file

it will be say song.mp3                                              .exe

but the .exe wont be visible necessarily.

Your virus scanner should pick these up.  Remember to keep it up to
date but i would suggest only downloading from sites that you trust.

Theoretically an MP3 file (or practically any file) that you process
could have some malicious content that would harm typical
installations today - today's security architecture baing utterly
laughable.  It's all a question of studying the MP3 players and
finding flaws in them - and then making carefully-prepared data files.

It's much easier to produce decoy files that are not what the title
suggests and flood networks withthese to discourage people from
spending time looking.

But with plenty of legal downloads around I can't see why you'd bother
with iffy ones.