Fat Daddios Pans---- I prefer to use 3" pans that don't have a seam in them just because it makes cleanup easier. The ones that I have are the 3" Fat Daddios, which bake nicely and keep the batter from overflowing if the layer is higher than 2". I have every size from 3" up to 16", and I find that it's good to have multiples of the 5"-9" sizes since those tend to be included in every cake combination. If you're baking more than one cake per week having multiples makes your life easier.
Agbay Single Blade Cake Leveler --- You don't NEED a cake leveler, but once you've used a good one you'll wonder why you didn't get it before. You can also get this in a smaller size and a double-bladed version, which are both listed on the page at the bottom. Don't waste your time with cheaper levelers, they'll just bring you sorrow.
Stainless Steel Scraper/Chopper--- I use a basic bench scraper for EVERYTHING. Cleaning the counter, smoothing icing, cutting fondant, etc. Make sure it's one that doesn't have a handle that extends past the blade part, you want it to be a 90-degree angle to make straight sides on your cakes.
Flexible cutting mats-- They're light, they're easy to move around, they're thin, they go in the dishwasher, you can cut them if you need a smaller piece. I put cakes on these to move them around while I'm working on them, they're very handy.
Bread Knife-- I use a bread knife to do pre-leveling leveling, trim sides, carve 3-D cakes. etc. it's also good for scraping crumbs off the counter if you use the flat back of the knife.
One-piece spatulas-- Silicone spatulas that don't have a separate handle are much better than the ones with plastic handles. You don't get a nasty buildup of gunk inside the handles, and the handles don't snap off while you're using them.
kitchenaid 6 quart mixer-- I have 3 of these and a Cuisinart 7 Quart , and I prefer the Kitchenaids because of the bowl shape.
A good Turntable--- I actually use a wooden lazy susan that has ball bearings in it, but any evenly-turning turntable without a lip on it will work. The weight rating and diameter are important so that you can put larger cakes on it.
Rainbow Dusts- These are food colors, edible luster paints and some glitters that are rated edible in the EU. I don't know if they're also FDA approved in the US, which is a separate process, but the edible paints give you a REALLY good metallic shine. They come in smallish bottles, but a little goes a long way.
Crystal Colors-- Excellent colors for gumpaste and they can be used for food coloring too since they're FDA approved for food use. Get these directly from the source at www.sugarpaste.com for the full range of colors or from my web store at www.acaketoremember.biz for a specific group at a discount (if I have them in stock!)
Offset spatula-- I actually like the smaller ones better, but I have a couple of sizes on hand at all times.
Drafting triangle--- Excellent for getting a straight edge on cakes when you're smoothing icing. The short end goes flat on the counter and the long end smooths the side of the tier.
Wilton Cake Marker--- Strangest thing ever, but I use it to mark the top edge of buttercream iced cakes to make sure it's even all the way around. Run it all around the cake and it will mark an even line in the buttercream to show where it needs to be levelled off for a uniform height.
Cable Cutter---If you use wooden or poly dowels, this will cut through them with no effort.
Sculpey Ball Tools--- Better than any gumpaste tools I've used.
Tylose-- I go through a ton of this when I make gumpaste or add a little into fondant to make it firmer.
Silicone pearl molds-- I use this to make pearls so that they're all the same size.
The Cake Bible--Excellent for recipes and basics of how recipes work. It also has a section for professionals for bulk baking and measurements.
Any Book By Alan Dunn--The best sugar flower books out there.
Some storage options that I use in my own house: Hang one of those back-of-the-door shoe holers with pockets. If you get one with clear pockets it can hold petal dusts, cutters, whatever small items you have knocking around.
Also for the back of the door are the rack systems, which could hold boxes with bottles of airbrush colors or bottles of dragees, tylose, etc.
To store cake pans, you can toss one of these dividers in a lower cabinet, stack the pans inside each other by size, then stack them in the dividers.
Or you can use one of these storage ottomans for pans that are stacked inside each other.
Here's a rack like the one that I have with bins on it.
And remember to label all of those bins with these dry erase markers and dry erase labels:
Small bead bins can hold piping tips or petal dusts: