Lots of options.... Timney, Jewel, and others make drop-in triggers. What's important, though is to note whether you have a M77 (tang safety) or a M77 Mark II (3-position bolt safety).
I have several M77 Mark II rifles all with different triggers. I installed a Jard trigger in one and it is awesome! I got the trigger in the classifeds here for $50. I took another one to my local gunsmith who did a trigger job for $35. The trigger on this one is also very nice. On my new Hawkeye that has the LC6 trigger, I installed a reduced pull trigger spring that made the trigger a lot nicer. For the price my local gunsmith charges, it is a no brainer. Hope this helps.
I thought about a timney for my mkii but the one I found only went as high as like 2.9 lbs. I wanted 3.5 and took it to a gunsmith for a little over $50 which is quite a bit less than the after market trigger. I think this is typical as it's really not a hard job from what I've heard. He also cleaned it up as far as creep and what not.