Vintage Stuff
http://www.network54.com/Forum/153652  - Forum for discussion of pre-war cards and related items
http://www.t206museum.com  - comprehensive t206 info, including back multipliers list
http://www.geocities.com/Heartland/Prairie/8980/trivia_pinkerton_collector_cards.htm - Pinkerton Card Page
http://www.efqreview.com/NewFiles/v17n3/onhistoricalground.html - Elysian Fields Quarterly-The Baseball Review
http://memory.loc.gov/ammem/bbhtml/bbcardsSets1.html  - Library of Congress site for very high-quality pre-WWI card images
http://www.vintagecardsonline.com/  - amazing vintage card gallery
http://www.oldcardboard.com (NEW LINK!) - fantastic place to begin learning about any pre-war card issue - items are being added to the site constantly
http://www.vcbc.com/ - Vintage & Classic Baseball Collector Magazine - Status uncertain
http://www.vintagecardboard.com (Updated Link!)- fantastic source of information for OBAKs and T3's
http://www.vintagecardboard.com/Ref_zee.asp (Updated Link!) - zeenuts site, including checklists
http://www.baseball-almanac.com/treasure/autont005.shtml  - interesting site
http://www.1919blacksox.com - Great Black Sox site!
http://blackbetsy.com/  - need I explain?
http://www.sportingnews.com/baseball/61/hbo.html  - not prewwII, but you have to see this movie!
http://www.toyou.com/fl/  - the Federal League!
http://thedeadballera.crosswinds.net/index2.html  - this is the weirdest vintage site you'll ever see, but engrossing!
http://www.thebaseballpage.com  - Occasionally some good vintage reading
http://www.baseball1.com/  - Some good vintage information and stats
http://tsn.sportingnews.com/archives/baseball.html  - The Sporting News vintage archive
 
Personal Collector sites
 
http://http://homepage.mac.com/thurber51/Personal38.html/  - Bruce Babcock's 19th century card site
http://www.geocities.com/mostly_rookies/  - Andy Baran's (collector) site
http://www.imageevent.com/crb972/ - Chris Bland's site - 19th and 20th century cards
http://www.sb1.50megs.com/catalog.html  - Scott Brockelman's site - big collector of Breisch Williams and Ramlys
http://www.caramel-cards.com/  Pete Calderon's Caramel site - the best!
http://www.geocities.com/brass_halo/CubanBaseball.html  - Ryan Christoff's Vintage Cuban Card Site
http://www.zmotive.com/gallery/jccards/ - Jim Clarke's site - vast collection of rare cards and terrific images
http://www.t207.com/  - Bill Cornell's site - great gallery of Fatima T222's
http://www.rbcraik.com  - Bob Craik's site
http://members.aol.com/METSBWD/hofers.html  - Brett Domue's card lists of pre-WWI HOF'ers
http://www.homestead.com/runscott/ - Scott Forrest's site - includes this links list
http://www.geocities.com/vintagesportscollector/homepage.html - Joe Kirchner's site - fantastic pre-war uniforms and equipment
http://http://members.shaw.ca/bluemanitou/ - Dan Koochin's site, featuring rare backs!
http://www.19cbb.com/ - Jimmy Leiderman's site: "19th Century Baseball Photographic Research"
http://www.lewisbaseballcards.com/  - Hal Lewis has a great site featuring graded HOF'er cards
http://www.freewebs.com/trib01vintage/ - Bryan Long's e-card sets
http://www.geocities.com/typecard777/Collection.html/ - Leon Luckey's site - lots of rare type cards, nice cards for sale
http://members.aol.com/rebelsart/ - Art Martineau's site - t206 expert
http://www.geocities.com/redmaccie/ - Brian McQueen's site: e-cards and type cards. Some cards for sale.
http://www.Cyscards.com/  - Cyril Petras' site, featuring '50s Topps and Bowman and sometimes older stuff
http://www.cycleback.com/  - vintage baseball memorabilia and cards - David Rudd
http://www.vintageball.com/  - Robert Silverman's site - fantastic baseball-related postcard collection
http://home.jam.rr.com/stutor/vintage%20baseball.htm - Sonny Tutor's site - tobbaco and caramel cards, and vintage gloves
http://members.aol.com/fkwcenturyold/Home.html  - Frank Ward's site - very unusual and rare cards
http://www.geocities.com/rhettmatthew_37/prewar.html/  - Rhett Yeakley's pre-war sports card site
 
Reference sites
 
http://www.retrosheet.org/index.html - Fantastic site loaded with stats and play-by-play accounts of pre-1984 games! 
http://cgi.cnnsi.com/baseball/mlb/all_time_stats/ - great site for player and team stats,any league,any year
http://www.pubdim.net/baseballlibrary/ballplayers/ - BaseballLibrary.com - stats and news stories where players are mentioned 
http://www.baseball-reference.com/ - more player and team stats
http://www.baseball1.com/c-stats.html - the Baseball Archive - great source for stats, any year
http://www.baseballhalloffame.org/ - Baseball Hall of Fame, not featuring Ed Reulbach
http://www.enel.net/beisbol/ - nice Spanish "Beisbol" site
 
Auction sites
 
http://thenational.net/index.cfm - The National Convention home page
http://www.collectibleclassicsauctions.com/- Collectible Classics Auctions
http://www.masstercards.com - James Verrill's site
http://www.festbergauction.com/  - David Festberg's new site
http://www.abouttimeauctions.com/index3.html - About Time Auctions - Jerry Smolin
http://www.tristarproductions.com/ - runs card shows around the U.S.
http://www.superiorsports.com/ - Superior auctions
 
Dealers
 
http://www.fullcountbcc.com/  Full Count - lots of nice graded cards
http://www.bmwcards.com - BMW Sportscards - best selection of really high-end graded cards
http://www.kityoung.com/  - KitYoung Cards
http://www.sportscardsplus.com/index.html - Sportscardsplus - good deals on commons
http://www.fritschcards.com/ - Larry Fritsch - good selection of vintage reprint sets
http://www.gfg.com/ - Dave's cards. Reasonable prices on lower-grade cards - usually plenty of caramel cards
http://www.mikewheatcards.com/ - Mike Wheat cards - reasonable prices on vg/vg+ commons - lots of caramel cards
http://dking-gallery.com/sports/ - Dennis King Galleries
 
 
Supplies and Grading
 
http://www.prograding.net/INDEX.HTM/ -Sorry, I couldn't resist.
http://www.beckett.com/ - Beckett publications and card-grading
http://www.collectorsuniverse.com/  - Collector's Universe (PSA card-grading,etc.)
http://www.ebaystores.com/id=731734 - JP Collector Supplies. Very reasonable and a great selection.
http://www.cardboardgold.com - Cardboard Gold - some of the best prices in the hobby for supplies