Star Wars action figures are arguably one of the most popular toys out there. Just take a look in the toy department of any big retail store (such as Walmart), or any big toy store such as KB Toys, and so on. But when it comes to finding the more rare star wars figures, the one that collectors often seek, where do you find them? Obviously older, more rare figures are no longer produced (otherwise they would not be very rare, and certainly would not be worth much money).
The first (and probably best place) to find the older, collectible figures is eBay.com. eBay is a great place to find a HUGE amount of used (and new) star wars figures. You can easily find many of the rare (and valuable) Star Wars action figures there. Heck, you can find pretty much ANY rare collectible item there; you will be amazed with the diversity. The second place that you can look to find used star wars toys (and figures) is Craigslist. However, do not expect to find nearly as much as you will find on eBay.
When it comes to buying rare action figures on eBay, make sure that you buy from a seller with a good feedback rating (preferably at least 100 or more, and with a 99% or better positive feedback rating). Also, be sure to fully read the auction description, especially when buying used toys (or figures). Many times a seller will only put a very brief and vague description in the title of the auction, and then they will put the more important details (and condition) about the item(s) in the actual auction details.
You may be able to get your hands on some decently valuable Star Wars action figures at garage sales or thrift stores, but the pickings can be slim to none, especially if you live in a remote area. Personally the only place that I would ever spend any time looking would be eBay. They have an amazing amount of collectibles; just be careful to buy from a trustworthy seller. As far as Craigslist goes, you just have to kind of use your own judgement, since they have no actual rating or feedback system.