I am planning to get Reason 6 sometime (hopefully before the summer is over), and I'd like to know, besides the Propellerheads website, where would I be able to get good free Reason Refills?

Reasonfreaks.com
Reaonfrance.fr
Puff.com
xsynth.com/examples.html
Reasonbanks.com

GOOGLE!!!!!!!!!

do you mean peff.com?

But you can always Puff with lotus2035 and a "Refill" your glass of wine

Rackflip is very good, although it's down temporarily for maintenance. The blog part is here:
http://blog.rackflip.com/

Also check Re-Wiki, which lets you browse for Refills and patches by various categories:
http://www.re-wiki.com/

If you need a large number of high-quality patches in one Refill, check:
http://bitley.laconicsounds.net/refills/platinum/

The main Propellerhead third-party Refill shop is actually decent:
https://www.propellerheads.se/shop/index.cfm?fuseaction=cate gory&Cat=4200&SortBy=Date

In my opinion, if you need a bunch of synth sounds, don't spend money on Nord/Korg/Moog/etc emulator Refills. Look for stuff like Tom Prichard's Refills that make creative use of Reason's built-in synths. They'll load faster, mix better, and sound more unique. My one exception is the Fairlight Refill I linked above, because it's so diverse. Look for Refills that could never be accomplished with Reason itself. This includes of course drum and loop samples, for which there are approximately eighty billion different Refills to check out...