e.l.f. Eyelash and Brow Wand ($1.00 on eyeslipsface.com and in Target Stores)
I'm of the opinion that everyone needs a spoolie brush. If you use brow powder or brow pencil, you need a basic spoolie to soften the look. If you applied too much mascara, you need a spoolie to brush out clumps (and it works better than the metal combs). For $1.00 you can't really go wrong.
Coastal Scents Fluff Pro Blending Fluff ($4.95 on Coastalscents.com)
There are a few vendors selling the same eyeshadow brush but I just listed Coastal Scents because that happened to be where I purchased it from. It's touted to be similar to the MAC 217 but I'm not 100% sure since I don't have the 217. Still though, this is actually one of my favorite brushes for applying and blending out cream eyeshadow and also for applying a transition color between the lid and browbone.
Loew Cornell Maxine's Mop 3/8 inch ($2.19 on Hofcraft.com)
This is a craft store brush and not the softest of the bunch but its shape is very similar to the MAC 239. It's a little fatter than the MAC 239 but the shape makes it good for packing and blending color onto the lid. This does need more conditioning than the rest of the brushes listed but it's still a good brush.
Sonia Kashuk Small Eyeshadow Brush ($4.99 on Target.com and in Target Stores)
It's a flat shader brush that's more slender than the Loew Cornell Maxine's Mop and softer. I prefer this when I'm doing a gradient on the eyelid with a lighter color on the inner third to a darker color on the outer third. It's made out of natural hair so it picks up eyeshadow brilliantly and the flat paddle shade means it doesn't fly all over the place.
Sonia Kashuk Bent Eyeliner Brush ($5.99 on Target.com and in Target Stores)
Another Sonia Kashuk favorite. I prefer gel and liquid liners over pencils (since it's usually easier for me to get a thinner line), so I'm a big fan of pairing them with this brush. I can get a very thin and precise line and the bend in the brush allows for a more natural grip and arm position.
So how about you? What are your must have eye brushes?