Sooo, I don't have cable TV, are there any affordable options for watching games (namely NBA and/or NFL games) on my computer? I think there's something on NBA.com, but it's like $100 for the year. I'm not sure if it would be worth it for me...but then again I'm not sure if there are any other more affordable options.

Anybody know of cheap/free methods of watching decent-quality games?

google justin tv.
it can be one of your amigos.

As xkrndreamer mentioned, justin.tv is a good site to check out some games.

Check out espn360.com for NBA games. It'll depend on your service provider whether or not you can actually watch, but if you can use it, it's a decent way to watch some games live. I've used it to watch some NBA and NCAA basketball and football.

i love wathcing volleyball games

there are loads of streamng options out there.......and huge list of sites that shows Video highlights of the games....

for soccer try this
http://www.lets-kickoff.blogspot.com

and for sports like Tennis cricket and soccer in general:

http://www.totalsportsmadness.com

I usually use myp2p.eu and the forums off of myp2p
They pool a bunch of different links for each game in case you have a preference (justintv, sopcast, tvu, etc)

I usually google stuff (when I want to watch F1 and I'm not at home) or listen to internet radio (Radio Le Mans). I didn't know about justin.tv, thank you!