I like the Layer Cake Shop online. I'm not sure how it compares price wise to other places but I like their selection and ways to search for things (ie, by theme or color).

Does it have to be online? I've found big-box craft stores like Michael's and AC Moore to be good sources of cake/cookie decorating supplies. They are not a good source for affordable bake ware.

Bed Bath and Beyond, World Market, and HomeGoods also frequently have unique/unusual decorating items for baked goods.

A regional resource that isn't available to most, Amish dry good stores carry cake and cookie decorating supplies in bulk packaging that is very affordable.

Resources, online, that I've used:
* King Arthur Flour Catalog (carries real chocolate jimmies and pearl sugar) (reliable)
* Kitchen Krafts (reliable)
* Fancy Flours (reliable)
* Chef Rubber

Resources, brick & mortar:
* Michael's Arts & Crafts
* Trader Joe's (was shocked they had pearls)
* Your neighborhood cake decorating shop or pro-chef store

Reasonably priced? Usually not - these things have a very high markup - and it's the shipping charges that are the choker when ordering online. I haven't discovered a true bargain source for prepared decorating materials so only buy the unusual ones and make my own colored sugars. You can take coarse grind, flake or granulated sugar (all of which can be bought in bulk) and tint it yourself using liquid or paste food colors (which one depends on the sugar). However, it's time consuming, so you might just consider buying those smaller easily-findable small jars of decoratives and packing all those supplies (except the pan) into an Anchor Hocking storage jar (available at Target, World Market, BB&B) - and make a beautiful label for it that says, for instance, "Maria's Cookie Jar". If you want to hide different labels, from various manufacturers on the decoratives, just put a sleeve of holiday paper over the manufacturer's label.

If you live around a Stop and Shop, look in the baked goods section. They usually sell seasonal sprinkles that they package themselves in small cookie tubs.

If you live on the west coast WINCO stores have a huge bulk section and they often have seasonal themed baking decorations (sometimes they're hard to find but look near candy or baking supplies.)

I have LOTS of experience with this. There's tons of reliable places out there, but you'll pay way more at some than others for no reason at all. For CHEAPEST places I use lots:

-http://www.thebakerskitchen.net/ (WAY cheapest I've found)
-http://www.countrykitchensa.com/

I actually would NOT recommend King Arthur Flour's site. For specialty flours and things, I'll find it there then google where I can get it cheaper. They all but double the price of things from other places you find, but they do have a good selection.

Bake It Pretty or Layer Cake Shop are what and what and have some cool stuff, but again, not for cheap. Nice assortment but you'll pay for it then plan on too high shipping prices.

Amazon is a great site if you know exactly what you need. Michaels is ok if you're using a coupon and not too picky (i.e.- you'll settle for just Wilton stuff)

Look up a local cake decorating shop by you. Almost every decent size town has one if you hunt and usually, they have good prices on lots of things (and are run by sweet old ladies that like cake!)