I play Tau, Guard, GKs, Sisters, and Tyranids.

I got $100 coming to me that I can spend on warhammer. That may not seem like a lot, but I'm broke and 95% of my collection was bought last millennia.

I like my Tau the way it is, I can't think of anything I really need to buy for it, so that's out.

My guard is okay, I run all infantry with a bane blade and I have more then enough bodies to do so. So I'm good there.

I'm not sure about my sisters. I got them in a trade and they don't have many special weapons and no heavy weapons on the girls. I only have 1 sisters rhino so I am a long way away from having a decent army. I'm more leaning towards holding off on getting any more in hopes of plastic sisters and a better codex. Because I would need to buy lots of sisters which are expensive and I don't have the cash flow to fund that.

As for my GKs, I've needed to buy a terminator box for a while to get the right bits and to get more terminators. I know that box would make me really happy. However, I can't shake the feeling that its a little redundant because I'm rarely out of terminators for my lists.
I'm also looking at a dreadknight because they're awesome! I think.
I'm also drooling over a Storm Raven which just seems too good not to take. Would love to drop off a dreadnought into combat! Just for the giggles!

My nids, I found a really nice and nasty way to play with the models I already have. Rush forward and just overwhelm my opponent. It works really well! But, I can still see ways of improving it.
I don't have any harpies/crones which seem to be the new black this edtion. They would really help me take out heavy armour.
I don't have any gargoyles which would fit perfectly with my army. Great screen for my rushing army!
I don't have a t-fex/tervigon which I keep eyeing for its power and utility.
I could get the hive/tyrant guard pack which would give me lots of bits and I can convert them to biovores if I wanted.

So, I'm at a lost. I'm definatly leaning towards a GK or Nid purchase. I just have no idea what to get.