i didnt read anyone elses reply so my info might've already been covered.
I lost my I-94, passport and social security card (they were all in one folder which i threw away while cleaning the house). You will need your I-94 for travelling. They asked for my I-94 when i was leaving US from the final port. but i guess you can tell them you lost it or something?? but you can't enter the country without an I-94.

The application process is pretty slow, it takes atleast 1 month to receive your I-94 and it costs $100+. INS never answers phone calls, i literally waited 2 hours to talk to one jerk who was in a hurry to hang up. anyway, as long as you have your legal documents and all that you should be able to get a new one issued. and if you have patience try calling them and asking them if it can be expedited..

good luck. i know how it feels to lose important document(s).