There are several online websites for Sports Memorabilia including www.sportsmemorabilia.com, www.allauthentic.com, www.authenticsportscollectibles.com.
The best site will depend on what sports you follow (Baseball, hockey, etc.) and whether or not you're interested in signed collectibles. GrandStandSports.com and AuthenticSignedSports.com are two places to start your search.
There are several local locations that may sell football memorabilia. Pawn shops, thrift stores, sports merchandise stores, or antique stores may also sell sports memorablia.
The best source to find the value of sports memorabilia is Heritage Sports Collectibles (http://www.heritagesportscollectibles.com). They have many prices listed and you can easily navigate to determine the pricing of your memorabilia. Comparing prices on Ebay can also give you a good general idea on the going price
One can find autograph memorabilia from a variety of different locations. One can try specialist sports auctions, a store dedicated to autograph memorabilia, or on online sites such as Autograph City.
Ebay or an auction
Pacers memorabilia can be found from the official Pacers club store. Alternatively, try sports stores in the local area, or webpages such as Amazon or Ebay.
There are many stores and websites that carry sports memorabilia. Sports stores such as Modell's, Sport Authority, and Dick's Sporting Goods usually have a wide range of sports memorabilia. One can also find great deals on websites such as eBay, where users sell coveted memorabilia for varying prices.
One of the best websites that sell Dr Who gifts and memorabilia is their own online store. You can also find some Dr Who items on Amazon.com if you want to compare prices.
Not easy to find and extremely rare, probably best bet is through online auctions.
In stores and online
There are many websites where one can find signed sports memorabilia for sale. Some examples include SportsMemorabilia, ProSportsMemorabilia, and SportSignings.
eBay or any sports memorabilia store.
Any cricket match that one attends they could find memorabilia at. There may be some sports stores that sell some but the best selection can only be found websites such as cricshop or cricketmemorabilia.