I'm not sure where you are in the USA, but out of Canada, flying to the UK, a lot of the 'charter' carriers offer pseudo-business class at a deep discount - Often at a cost of only a couple of hundred dollars above a regular ticket. Perhaps similar companies operate out of the UK to the USA?

For example:

http://www.airtransat.ca/en/4_3.asp

Also, United Airlines offers "Economy Plus", referred to here as E+. I'm 6'2, so I find the few extra inches of legroom that comes with E+ well worth it. You can often purchase an upgrade to E+ as part of your ticket for not a lot of money. Details are here:

http://www.united.com/page/article/0,6722,1314,00.html

British Airways also has a "deluxe economy" product that is cheaper than business class, however it's quite a bit more money than United's E+.