The <insert colour here> Box I reckon.
HL2: EP1 + 2
HL2: EP3
Portal 2
Some TF2 expansion or new game
I doubt they'll bundle a L4D game/expansion in there as that game is worth too much on it's own.
edit - and Mac Steam users will get it "on a Wednesday" at some point in the future (6th June 2063 at a guess).
More like, HL2, HL2:ep 1, HL2:ep 2, HL: ep 3, Portal 2, portal 1, TF2, L4d, Counterstrike and HL1 source version and the original Lemmings and Worms, for £75, but its cheap because look how many games you get... yay.
HL2 is old, boring and dead, and I'm getting a touch peeved at having to pay for content I have to get the new bit of it, or get utterly utterly screwed on the single item price.
I have such little interest in Ep 3 now, HL3, a new game, new engine and some new ideas would be interesting, a new CS would be great, Portal was good but I'm not killing myself waiting for a second 1 hour long game(maybe 2) of puzzles that only felt new because we hadn't seen them for so long, but were really incredibly old and basic. THe novelty of an updated incredibly old style of puzzle game won't be there this time.
A new CS or Hl3, anything else is almost boring.