I did a quick search on eBay the other night for Pokemon cards, just to see if any good deals could be found. Generally speaking, Pokemon Ex, Pokemon Lv. X, Shining Pokemon, Pokemon G, and any other Holographic (aka "shiny") card is worth at least something.
I filtered my search to "ending soonest", and came upon these two cards, both from the same seller (got to save money on shipping!).
Machamp: $10.50
Charizard: $1.04
Shipping: $3.00
Total: $14.54
Now, what are they worth? (I price via the cheapest Buy-It-Now, shipping included).
Charizard G LV X. = $7.00
Machamp Prime = $15.05
So, when it comes down to it, I will make about $7.50 before shipping and handling. Doesn't seem like a lot, but if you grab a couple cards for cheap like this, and turn around and flip them, it adds up.
You literally could start your eBay business with $20!