Learn English – “When responding, please reference the claim number”

In addition to using Mark Hubbard’s “Thank you in advance for [keeping me informed]” (or just “Thanks in advance for [ … ]” in less formal situations) to express your thanks in advance without having to rely on context, you could also consider using a near-synonym for being thankful to use with the conditional would, for example:

“I would (I’d)[ greatly/very much] appreciate your keeping me informed.”

or (to emphasize the conditional notion even further):

“I’d be [extremely/very] grateful if you would (you’d)/could keep me informed.”

(Please note that, although it’s probably overstating the actual level of appreciation/gratitude, I think I would include greatly and extremely, especially in the above, “in advance” cases, but probably less so in the “after the fact” cases mentioned below. However, be careful not to “over-do” it because you could come across as being sarcastic or “sycophantic” [the English sense!], so on second thought, maybe the more restrained very/very much would be better in these cases where intensifying the gratitude might be in order because you are actually requesting a future favor at the same time.)

Regarding “after the fact” expressions of thankfulness (such as the one you made on “Overflow” and are asking about here), in addition to Mark’s use of the past tense (provided) or relying solely on context (which I agree can be ambiguous, especially in your example where it could easily be interpreted as an on-going request), you could consider changing “keeping” to “having kept” and “keep” to “kept” to use either with the same near-synonyms above (but in the unconditional present) or else (preferably, I think) simply with the original “Thank you/Thanks” construction, for example:

“I [do] [greatly/very much] appreciate your having kept me informed.”
(where the do would be an optional way to emphasize the appreciation)

“I am (I’m) [extremely/very] grateful that you kept me informed.”

Thank you (Thanks) for having kept me informed.

(But please see this relevant Word Reference thread that seems to confirm that we are, in fact, often (but not always?) at the mercy of sometimes ambiguous context in English (as indicated in user3169's answer). At least “Kelly B” begins his/her answer with “Yes, that's right,” so making the effort in our own speech to avoid the ambiguity would be not only admirable, but also grammatically and logically correct, although we'd still have to rely on context to interpret the meaning when spoken to us by somebody who is less concerned with clarity.)

Do you know when the package is expected to be shipped?

When is the expected date for the package to be shipped?

Both of these are acceptable. The term you're looking for, I think, is passive voice since "is expected" and "to be shipped" are in the passive form of the verbs "to expect" and "to ship":

They expect that I will ship the package

It is expected (by them) that the package will be shipped (by me)

To answer your question about other ways to say this, the passive form of the verb sounds somewhat more polite than the active form. If you don't care about politeness, you can use the active voice:

Do you know when you expect to ship the package?

What is the expected date you will ship the package?

or even more direct:

When are you going to ship the package?

There are, of course, many other verbs you can use to express the same concept:

When do you plan to mail me the package?

When do you think you will deliver the package?

When do you anticipate the package will arrive?

And so on.

Final note: In your second sentence "expected" is not the past tense of "to expect". It's the adjective form of "expect" that modifies the noun "date": "the expected date"