In 3rd edition, you could ready a partial charge. From the PHB, p134:
Only partial actions can be readied. To do so, specify the partial action you will take and the conditions under which you will take it.
Also, PHB p121:
As a general rule, you can do as much with a partial action as you could with a standard action minus a move. Thus, you can attack once as a partial action or move your speed, but you can’t both move and attack unless you are performing a partial charge action.
In 3.5 edition, there is no such thing as a partial action. Readied actions are described thusly (PHB p160):
You can ready a standard action, a move action, or a free action ... You can take a 5-foot step as part of your readied action, but only if you don’t otherwise move any distance during the round. For instance, if you move up to an open door and then ready an action to swing your sword at whatever comes near, you can’t take a 5-foot step along with the readied action (since you’ve already moved in this round).
On the other hand, there is also this:
If you are able to take only a standard action or a move action on your turn, you can still charge, but you are only allowed to move up to your speed (instead of up to double your speed). You can’t use this option unless you are restricted to taking only a standard action or move action on your turn (such as during a surprise round).
So you can definitely charge during a surprise round, but what about as a readied action? It appears to meet the criteria of situations where you are restricted to only a standard action or a move action, but the wording still seems a bit ambiguous to me.