The 'limited edition'

Ico – PS2
When Shadow of the Colossus came out, it's predecessor was given a re-release, as its sales were initially poor (much like Okami, really).

Of course, it's an incredible game, as anyone who has played it will attest. But the re-release was issued in a standard DVD case, whereas that initial production run saw cardboard cases with limited edition art cards. Limited edition art cards!

The re-release has knocked a tenner off the average eBay price, as they were going for £40 a time. You can now get hold of the UK version for £30 pretty easily. Ironic, however, to note that it's one of the few examples of games that are genuinely worth their original RRP. Crazy, huh?
Average eBay price: £30 (about $60)

Valkyrie Profile – PSone
This limited edition NTSC PSone game fetched £114.95 on eBay. It took a second listing for it to sell at that rather ambitious Buy it Now price, but we're impressed the seller stuck to their guns. It does look gorgeous.
eBay price: £115 (about $230)

Sonic Adventure 2 – Dreamcast
This limited edition pack was only available at retail for two days in Japan, released to coincide with the tenth anniversary of the release of Sonic 1. Even though it's getting on for another seven years past the release of Sonic Adventure 2, prices are still modest for the limited edition pack, likely due to the fact it's quite common to find it when you look.
Average eBay price: £15 (about $30)

World of Warcraft: Burning Crusade Collector's Edition – PC
For all the millions of WoW players out there, the number of unopened, special edition boxed copies of the game are pretty few. And why shouldn't they be valuable? WoW is a phenomenon - just imagine 50 years down the line, when we're all linked directly into the internet and scoff at when games used to come on physical media. An unopened special edition copy of one of the games that triggered a collective shift towards online play (or mass divorce) is going to be worth thousands. Now? £70 ($140).
Average eBay price: £70 (about $140)