Before we get into the list, please visit your friendly local game store and investigate their prices. Smaller stores tend to have lower overhead costs than larger stores, and they pass the savings on to the customer. Spend some time chatting with store owners; I've gotten discounts on purchasing several items simultaneously. Friendly local game stores are also a great way to meet other people that like to play board games, and some stores have regularly gaming nights. (Find out which nights are board gaming nights vs. Magic the Gathering; showing up on Magic the Gathering night is awkward.)
Now that you know what the prices are like at your friendly local game store, we invite you to check out the following on-line retailers. On-line retailers have even lower overhead, but you have to pay shipping costs. Calculate the total cost and see what makes the most sense based on where you live. (If you live in an area with no local game stores, the answer will be fairly obvious.)
If you live in North America, I suggest that you support our forum member Carcatronn and buy from his on-line store. He has most of the games, expansions, accessories, and spare parts. He also provides bundle deals that can't be found anywhere else. If you live in Canada (like me), contact him before purchasing to save on shipping cost.
http://www.carcassonneshoppe.com/ - Store closed down
Hans-im-Gluck has an on-line store with many games, expansions, accessories, and spare parts. Several items cannot be found anywhere else. The site is in German, so you'll need to translate some words. If you have Google Chrome, it can automatically translate the pages to English.
http://www.cundco.de/
MeepleSource has a large selection of wooden parts for Carcassonne, as well as apparel and some other things. A few times per year they have sales, which you can find out about by subscribing to their newsletter or "liking" the CarcassonneCentral Facebook page.
http://www.meeplesource.com/index.php?PARTNER=carccentral
I was recently referred to the following company in the United Kingdom which has a wide variety of drawstring bags, for those who want to upgrade their meeple storage to something fancier, or maybe you've outgrown your tile bag and need something larger.
Cleverbaggers mini size bag is 6cm x 9cm. This would probably hold a set of meeples snugly. The "smaller" size 10cm x 13cm might be better suited. The 10cm x 13cm bag should also work well for the tower pieces.
The regular Carcassonne tile bag is 20.5cm x 26.4cm. CleverBaggers regular size bag is 25cm x 35cm, and the large size bag is 38cm x 43cm. If those are still not big enough for your game of MegaCarcassonne, they also have larger sizes, though in fewer color options.
Also worth mentioning that they can do custom printing on the bags for an additional charge. (no minimum order quantity)
http://thecleverbaggers.co.uk/bags/drawstring-bags
FunAgain Games is recommended by several of our forum members. They have good prices on the games and expansions, if you live in the United States or close enough to the border that you have a US mailing address.
http://www.funagain.com/
For games and expansions that are out of print, check the marketplace on BoardGameGeek AND check eBay. Do both of those things and compare prices. Some people ask way too much money for things. You're looking for people that have lost interest in a game and want it to go to a good home, rather than the thrift store profiteers who buy games for $2 and sell them for $40.
When you are browsing on eBay, keep a watchful eye. Some people, either in ignorance or defiance of the law, sell fan-made expansions. DO NOT BUY FAN-MADE EXPANSIONS. Only buy official Carcassonne merchandise. Selling fan-made expansions is not permitted by Hans-im-Gluck. If you see somebody selling a fan-made expansion, report them to eBay and notify the author of the expansion (which usually is somebody from here). Also notify myself and/or Kettlefish so that we can inform Hans-im-Gluck.
Here are some other suppliers of wooden bits (in case you need something for a fan-made expansion):
http://www.spielematerial.de/en/http://www.miniongames.com/accessories/boardgame-parts.html http://www.rpgshop.com/accessories/boardgame-parts/http://www.boardsandbits.com/Linkback: https://www.carcassonnecentral.com/community/index.php?topic=30.0