Picking a frame

A great thing to do is to modernize an older bike. There are purists who say not to do that to a classic. Generally, I would agree as there are still tires and parts to keep these things serviceable while retaining their collector value. On the other hand, you have to do what will keep you riding. Paying the LBS to add a new group and letting them keep the "old junk" is a complete no-no. The truth is there are many older classic bikes out there that have been broken apart for profit. You see tons of classic frames and parts for sale on forums, lists, and Ebay. Put them all together and you'll have lots of classic bikes but still a lot of leftovers. I say use them just don't be part of the problem buy being such a hack. So if you modernize, keep and lable the parts so that they can return home when the time is come.
You have to decide what frame you want to hang all your parts on. Most mid-level frames today are mass-produced aluminum. The higher end stuff starts to add carbon forks and seat stays, then eventually they go all carbon. The days of handbuilt frames in the local peloton are essentially over. There are still great framemakers out there if you can afford them, and handbuilt framemaking is truly an art. Buying an older handbuilt frame, though still expensive, is an option.
If you are stuck on an Italian, French, or say Belgian frame, good luck. Most famous brands have long since been bought up and are now part of a conglomerate of brands. Because of outsourceing, even Trek(the great american bicycle company) has a majority of their frames built overseas. Your favorite manufacturer is likely no different. I'm told Trek actually owns their overseas factories so quality can be better controlled but this is hearsay. Unless you buy the top Trek, it's made in China or Taiwan as I have seen both.
Companies like Kinesis(Taiwan and maybe elsewhere) makes frames for many competing brands here in the USA. Basically what it boils down to is you have to decide what name you like on your shiny new Kinesis frame. A similar practice actually goes way back to handmade Italian frame days. Many winning GdI and TdF bikes were painted and relabelled differently than their actual builder. Fair game to this day, I guess.
I liked the Masi name on my new 0 miles 2006 Kinesis frame. I got it off Ebay and it came with a carbon fork and headset for around $200. It is new, straight(go look at a WalMart bike!), as light and high tech as the next guy's, a bit different, and I like Masi(or at least what Masi once was). Pick your brand and look around. There is a price point for everybody.