The info about putting money in your 401K up to 3 years after the return is true. This is what I did (after maxing out the TSP as others have said).
Also, don't forget the Deposit Savings Plan. This is available to all personnel deployed to combat zones. You can put the equivalent of one months salary at a time, up to a total of $10,000 dollars in this. It earns 10% interest (not tax free). Must be withdrawn 90 days after returning. I put in $10,000 (two instalments to meet the max pay check requirement), when I was boots on the ground; I got over $11,000 back one year and 90 days later. Not bad for a plan where you principle is safe.
Finally, if you have been putting your money in a regular IRA, consider rolling it over to a ROTH while you are deployed. You will pay tax on the roll over, but your rate will probably be much lower since most of your pay is not taxed.
And after the TSP, 401K, don't forget to contribute to the ROTH.