Google has redesigned it's Android Market to allow you download and buy apps from your personal computer with a you web browser. The Android Market can be found at http://market.android.com. The new marketplace allows users to install apps downloaded from Web to their smartphones and tablets.
You do not need an Android with a SIM card to access the new marketplace, which I guess is intended for upcoming tablets which will not have come with 3G, and hence no SIM card in the device. All you need to get access is log in using your Google account. When you log in to the Android Market, you should used the same account that's you used with your mobile device, since your apps are synced directly to that Gmail account.