Major Collector Forums
Collector's Universe - Ground zero for all USA paper money talk. Meet other paper money enthusiasts from around the country (and world). Great discussions about grading, upcoming auctions, and industry news.
CoinTalk.com Paper Money Forum - Although much of this website is dedicated to coins, there is a forum organized for World and USA paper money fans. Great place to discuss new findings. Also, there is a small advertising section for dealers/auctioneers.
Coin Community Paper Money Forum - CoinCommunity.com offers a friendly atmosphere and gathering place for paper money aficionados. Common discussions include: What's it Worth?, Rare notes, interesting finds, and eBay auctions. An active community.
CoinPeople.com US and World Currency Forum - This exciting forum offers links to various types of bank notes, noteworthy "Notes in the News", and a virtual museum of currency. Fun and friendly forum.
Collecting Banter Paper Money Forum - Although this forum contains mixed discussion of both World Paper Money and USA paper money, it's still worth a visit. Some threads are in foreign languages, which is helpful for those that speak English as a second language.