Hi TFC,
Geez I haven't been over here in moons... someone sent me a link so I dropped in. I created a complete course on spread trading a few months ago. I agree with Older Than Dirt on both counts, the volatility these days makes spreading much more "interesting" than it used to be and also is much more manageable than flat price trading. And spreads do reveal a lot about the dynamics of the underlying markets.
Having spread charts available is a great idea, in fact the major impetus to starting the spread newsletter was that there is a complete vacuum of data and info on the subject. After the 100th time I had to send a chart to somebody because they couldn't find one... realized there is very much a need. I will definitely send my readers here to get charts when you're up and running, thanks!
Some suggested spreads. First and foremost the wheat complex- MGEX. KCBT, CBOT -combinations are really great spread markets. Correlated and I daresay predictable to some degree. I would encourage having a "multiplier" option so that we can plot 2 corn vs 1 soybean, etc. Platinum/gold is one of my current obsessions, check that one out. Inverted for the first time, ever I think, but at least as far back as I have been able to look. Plat went from $1400 over gold to $200 under. It is about $150 under now, historically is has tended to stay $100-400 an ounce above gold. I suspect it will return there soon enough.
I like Matt's suggestions (have to look up Black Sea, new to me...is it eurex?). Calendar spreads in the grains (I'm sure you'd include these), ho/rbob of course, meal/oil (outright 1:1's to compliment the crack and crush, which are a little big for most specs to put on). Wheat/corn has been a great one this year. Feeder cattle/Live Cattle too of course. For academic purposes, gold/crude values and gold to S&P (point basis) are always interesting. Along those lines ES/NQ can be revealing for stock sentiment/direction.
Later...
PS- Just saw the link to URL option below so added my site (I'm assuming that is what it's for, if not just delete it I won't be offended....thanks)