Although getting rarer and rarer on the 2nd hand market these days, if you want to go down the steel route I can't recommend the Fort CX frame built in Columbus Foco highly enough - bags of clearance for modern tyres and a great ride to boot. Had mine 7 years or so now (bought it used in late 2004) and it's still going strong albeit with a respray last summer. Raleigh RSP cross frames in 853 tubing are also worth keeping an eye out for.
David
David