RailEurope, oft maligned by Fodorites for inflated ticket prices, which is often the case in point-point tickets in many countries, has, however, great Eurostar tickets London-Paris/Brussels- after three years of stagnant fares RE just revised Eurostar fares:
A quick look at some new fares:
$70 round trips
$89 one ways (yes more expensive than round trips!
$159 one way first class tickets
$140 return first class tickets
(All first class tickets give a fairly good meal with wine, etc. before and haven't looked at fine print to see if so with these fares)
$88 day returns (down from $94)
$98 first class day returns - incredible bargains (haven't looked at fine print to see if this includes meals - if so a great deal
$77 each way passholder fares (often more available than cheaper $70 return fare)
$136-147 one way first class pass holder fares
$89 youth fares one way for under 26 ages
Add a $15 booking fee per order and a $15 mailing fee from RailEurope if total order under $200 and i think a $25 fee if you want to talk to someone when ordering - if not ordering online. As always i recommend BETS (800-441-2387) for Eurostar expertise in my long experience with them - RE agent - same prices but free to talk to someone. Or www.eurail.com or www.raileurope.com
Anyways the dirt cheap $70 return or $89 one ways are in very limited numbers of available seats - can book up to 6 months in advance and to get cheap fares must do so - could pay lots more if just show up.
This is from a cursory look at the new prices and i'll take a more detailed look - please correct me if i missed something or read something wrong!

Youth Fare Clarification: i wrote $89 each way but that's the top fare on a few trains, many more can be had at $70 or $53 for those under 26.

Hmmmm...when I looked at these, the prices posted appeared to be one half of the return price. In otherwords, when you selected the return time you saw $88 too Then when you selected it, the fare went from $88 to $176 total.

You may be right but i did that and it said return - but this makes more sense - i was really surprised by how low they were - double it and makes more sense. Thanks i'll take another look. I couldn't figure out why one ways would be more expensive than returns.

Erico Smith:
You are exactly right - i'm a Dumbkoph (sp?) - but the site is confusing as on one page it has checked round trip and then gives a price - but you are right this is the price for going and would be added to the price for returning to get total price.
One way prices i give are obviously one ways.
So the bargain round trips are much less a bargain than i (too) quickly surmised!

Oh bummer.. . I got excited for a sec!