You have a number of options.
First, if you have a camcorder with Digital video out and analog in, you can use it to transfer from the VCR to the Mac. Older camcorders (like mine) don't allow both interfaces to be used at one time, so I need to tape the VCR tape onto a DV tape, then transfer that DV tape to the Mac.
There are various analog->digital converter boxes out there as well. HOWEVER, the cheaper ones tend to have the audio drift out of sync with the video on longer segments, so beware.
There are also, I think, dedicated cards for this, but then, if you buy a different Mac, you might not be able to use the card, whereas the external solutions are not going to be a problem.