Formal:
* Proved useful
* Was of assistance
* Served a purpose
* Was beneficial
* Was invaluable
* Was indispensable
Informal:
* Was a lifesaver
* Came in clutch
* Was a godsend
* Was just what I needed
* Was a real help
* Saved the day
* Was a blessing
Figurative:
* Was like a magic bullet
* Hit the spot
* Was exactly what the doctor ordered
* Was like finding a needle in a haystack
The best alternative will depend on the context and the tone you want to convey.