How can I put a preset ending on my emails that will appear every time?

You can set it up here under "Signature":
http://mail.google.com/mail/#settings

Or you could used this addon:
https://addons.mozilla.org/en-US/firefox/addon/7757 (requires an account for mozilla.org as it's experimental) and include, links, images in your signature.

?why? Email signatures are the hallmark of newbeness, nuisance, cluelessness, compensation for insecure, yet overblown ego, and generally juvenile behaviour (then again, maybe you are a yuvenile to begin with). It's egopuffery at its worst, make-believe "letterhead" interesting in the first 15 emails or so. Your steady correspondents will soon tire of it, don't need it anyway, and the occassional ones couldn't care less about your many home/ business/ mobile fax and phone numbers; your street address' number equal to that of Elvis; car make and/or the status of your HIV-positivity. So why bother?