Before this is done at the table, talk to the DM and the other players. Be up front about what's going to happen: the character will, often during each encounter, be taking up to four standard actions pretty much in a row. First, the DM must be made aware of this so that she can account for creatures doing this. (Typically, what the PCs do the DM can also do, and the campaign setting may not have been designed with this in mind.) Second, the other players should be made aware that the character will be taking up a lot of game time. The other players should be prepared beforehand for their characters to be inconsequential for upwards of 20 min. while the DM adjudicates the character's multiple actions. Neither prospect may sit well. Abstractly and mechanically, taking a bunch of extra actions is awesome, but concretely and socially? Perhaps not so much.

Confirmation: A step-by-step example of one possible sequence

In the morning, a caster casts the 5th-level Sor/Wiz spell contingency [evoc] (Player's Handbook 213), picks as the companion spell the 4th-level Sor/Wiz spell celerity [trans] (Player's Handbook II 105), and picks as a condition something like Upon resolving the action granted by the second celerity spell that I cast in a round beginning on my turn. (A player can pick almost anything as a contingency spell's condition, but the DM determines if the condition is appropriate; see here.)

Later, during an encounter, on her turn the caster takes a standard action to cast a spell, takes a move action to move up to her speed, then takes a swift action to cast a celerity spell ("Using an immediate action on your turn counts as your swift action for that turn" (Rules Compendium 7)). She then takes the granted standard action as if she had readied an action. Normally, at the conclusion of this last action, the caster would gain the condition dazed (Player's Handbook 307), but the caster is immune to this condition. (N.b. Gaining immunity to the dazed condition tends to be resource-intensive.) Then her turn ends, and it's the next creature's turn.

At this point, a prescriptive reading of the celerity spell would limit the spell to being cast in response to a DM-approved stimulus because the standard action granted by the celerity spell is as if the caster had readied an action. However, a descriptive reading of the celerity spell—that reads its reference to the ready action as a comparison—allows the caster to cast to cast the celerity spell pretty much whenever, ready action trigger be damned. Either way, shortly after taking her second standard action the caster takes an immediate action to cast another celerity spell and takes this round her third standard action—this one, too, as if she had readied an action. (Taking an immediate action this way to cast this celerity spell—her second in the round that began with her turn—exhausts her next turn's swift action.)

Then, when that granted action is resolved, the contingency spell's condition is met, and the contingency spell's companion celerity spell is cast. The caster takes another standard action—her fourth this round—as if she had readied an action.

Note: The Lords of Madness feat Quick Recovery (181) is no help in resisting the dazed condition when chaining celerity spells: It's benefit kicks in specifically at the beginning of a creature's turn. What's needed is the Dragonmarked feat Mark of the Dauntless (142), but its prerequisite of a true dragonmark might make it unavailable in some campaigns.