I usually have GMail fired up on my laptop anyways, so I simply create a new mail, then paste the text into the e-mail body and save it as a draft.
I go to the other computer, open up the draft, and copy the contents to the clipboard.
Other options do exist (such as X2VNC and friends), but don't always work too well between platforms for clipboard activity. Note, you can also use file attachments in a draft.
You can do this with pretty much any web mail client that supports drafts, and it's not quite as cumbersome as actually e-mailing yourself. You can just trash the draft when you're done, or use a draft as a transient scratch pad for data you wish to access from multiple computers.