Cheapskate option: Use your PS3 to download movies and trailers. Buy a 16GB memory card (or do a d21lewis and use an external HDD--big enough to use with your 360, PS3, and PC!! Only 16GB can be used with the 360, though. Microsoft restrictions). You'll have to play games from the disc instead of installing them, though. Use the Memory Card of HDD to save your Live Arcade games and any trailers/videos/demos/etc. You may want. Use the console's memory to save your game saves.
-Installing really does make a difference in loading times. In a few games, it's cuts the load times from around 30 seconds to about 5 seconds!! Some people claim there's no difference in playing from the disc to the HDD but I've seen this firsthand. I should post a video on youtube--and maybe I will.
You go the cheap route now if money is an issue. Get the HDD later, even though it will cost you more money in the long run. Enjoy your two systems. They share a lot of the same games but they still have very different identities. You're gonna love it!
* I use a 500gb Seagate FreeAgent HDD. I recommend it because it's very cheap and very reliable. Everything that uses an HDD used it in my house. I even downloaded trailers from the PS3's PSN and watched them on my 360. I take videos from my PC and watch them on my consoles. Good thing to have and it's very tiny, too!
