Paid apps can't be moved, technically, since it's linked to the google account you purchased on.
Now with Titanium Back-up Pro that would be an easy way. Just back-up everything, then switch google accounts and restore with TiBu, and then logging into the market with your new Gmail should sync everything with the new account.
Alternatively, a free solution would be to sync with AppBrain (sign in using a non-Google account!). When you sync, it will save a list of all apps on your device. Change gmail accounts and then re-sync (you'll then have to "copy" all apps from the other load to install with your new account). Along with Appbrain, you also want to install Fastweb Installer, which allows bulk restore of apps from the market thru AppBrain.
I imagine any paid apps you have will cause a hiccup transferring to the new account. Perhaps Google can help you there, but I doubt it. I don't know if you use TiBu to "hack" that if the market will let you install/update those apps that it doesn't recognize that gmail account as having paid for.