Look for British steel with chainstays at least 43cm and good tire clearances. Some marquees to keep an eye out for:
Bob Jackson
Claud Butler
Mercian
Woodrup
Holdsworth
Dawes
and more:
http://www.classicrendezvous.com/Bri...es/British.htm
Raleigh International is a popular, abundant option. Schwinn Paramount P15 would be nice, but may not fit your budget. Trek made several 'sport touring' models that would fit your needs. And as wrk101 suggests, there are many, many Japanese built frames that would fit the bill, and would be easy on the wallet.
Many other options out there. Again, look for longish chainstays, good tire clearances, and be sure to inquire about threading. If you want a modern build, stay away from French and Swiss. Be aware that many older frames don't have drilling for recessed brake nuts, so you'll have to drill yourself or find a work around. Also, many of the older frames have fewer braze-ons for convenience. You may also find you have to respace the rear drops for a 130mm hub.
Here's my Japanese built Raleigh International Mk. II:
