ND filters are probably going to be the best suggestion, but i'll leave it up to others to say which values are the best.
To avoid damaging your eyes, use live-view, but then you'll cook your sensor instead.
With a canon EF mount lens on live-view, the camera will automatically stop-down the lens on live-view if there's too much light coming in (assuming the narrowest aperture is small enough). But with a manual lens via adapter you can set the aperture to smallest anyway, and if that's small enough then you can use it on live-view or viewfinder just the same.
And for the hell of it, here's a shot I took last eclipse, January 2011, 7D, EF-s 15-85, 85mm, f/20, 1/4000s, iso100:
I didn't have it at the time, but next time I would take this shot with my ND400 (9 stops), which would go down to f/5.6 (4 stops) and bring the shutter down to 1/125 (5 stops) (if my maths is correct).
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