The Shimano M324 pedals work well and aren't too expensive new. Their advantage is that the other side is a standard cage so you don't have to wear SPD shoes to ride. They are fairly heavy.

The A600 pedals are very nice but pricier than the M324 - much lighter too.

Another SPD pedal you should consider is the Xpedo M-FORCE 3. They look good on classic bikes as they are silver, and they work very well. They're double sided, so you can clip in on either side of the pedal, might be a little easier than the M324 or the A600 as those only have one-sided SPD clips.