The Collaborative International Dictionary of English v.0.48:

Indeed \In*deed"\, adv. [Prep. in + deed.]
   In reality; in truth; in fact; verily; truly; -- used in a
   variety of senses. Esp.:
   (a) Denoting emphasis; as, indeed it is so.
   (b) Denoting concession or admission; as, indeed, you are
       right.
   (c) Denoting surprise; as, indeed, is it you? Its meaning is
       not intrinsic or fixed, but depends largely on the form
       of expression which it accompanies.
       [1913 Webster]

             The carnal mind is enmity against God; for it is
             not subject to the law of God, neither indeed can
             be.                                  --Rom. viii.
                                                  7.
       [1913 Webster]

             I were a beast indeed to do you wrong. --Dryden.
       [1913 Webster]

             There is, indeed, no great pleasure in visiting
             these magazines of war.              --Addison.
       [1913 Webster]

WordNet (r) 3.0 (2006):

indeed
    adv 1: in truth (often tends to intensify); "they said the car
           would break down and indeed it did"; "it is very cold
           indeed"; "was indeed grateful"; "indeed, the rain may
           still come"; "he did so do it!" [syn: indeed, so]
    2: (used as an interjection) an expression of surprise or
       skepticism or irony etc.; "Wants to marry the butler?
       Indeed!"

Moby Thesaurus II by Grady Ward, 1.0:

125 Moby Thesaurus words for "indeed":
   OK, Roger, a fortiori, above all, absolutely, actually,
   all joking aside, all right, all the more, alright, alrighty, amen,
   and no mistake, as you say, assuredly, at all events, at any rate,
   aye, by all means, certainly, chiefly, clearly, da, decidedly,
   decisively, definitely, demonstrably, distinctly, dominantly,
   doubtlessly, easily, especially, even, ever so, exactly, factually,
   fine, first of all, for a certainty, for a fact, for certain,
   for real, for sure, forsooth, good, good enough, hear,
   historically, in all conscience, in chief, in fact, in reality,
   in the main, in truth, in very sooth, indeedy, indubitably, ja,
   just so, mainly, mais oui, manifestly, more than ever,
   most assuredly, most certainly, mostly, naturally, naturellement,
   nay, never so, no end, nothing else but, noticeably, observably,
   obviously, of a truth, of course, okay, oui, particularly,
   patently, peculiarly, positively, precisely, predominantly,
   primarily, principally, quite, rather, really, really-truly, right,
   righto, sensibly, seriously, still, still more, sure, sure thing,
   surely, to a certainty, to be sure, truly, truthfully,
   unambiguously, undeniably, undoubtedly, unequivocally,
   unmistakably, verily, veritably, very well, visibly, well and good,
   why yes, with truth, without doubt, yea, yeah, yep, yes,
   yes indeed, yes indeedy, yes sir, yes sirree