Trade it in for a PS3, if you definetely want to trade it in. You get a lot more memory, blue-ray, built in wireless. And did I mention, almost every game for Xbox 360, comes out for PS3? Except for Xbox 360 exclusives like halo 2 and 3. I never liked the halo franchise though. But let me do the math for you:
20GB Xbox 360=
250$(249.99$) for the system.
Hdmi cable (for hd tvs)= about $100
Wireless card = About $100 (if you don't want too hook it up via wire to your router or modem)
Games = Usually about $30-$60 each
Features DVD capability
Xbox live account = About $4-5 a month, $48-60 a year.
Total with one new game, hdmi cable, wireless card, and xbox live account for a total year =
Around $568 or $570
80GB PS3
PS3: $400 ($399)
Comes with built in wireless card
Free online
Game are about 30-60$
Features Blu-Ray
Plays DVDs (maybe in HD)
Hdmi cable (for hd tvs) about $100
Total=
1 new game, hdmi cable=
$560
PS3 is cheaper in this equasion.
(prices based off of amazon.com)