Replacement for Suntour NCX-410 crankset on commuter bike? I've had a 2007 Marin Larkspur which I have been using as a commuter and recreation bicycle for 3.5 years. For the past year, I've been slowly learning to do my own repairs and upgrades as they have come up. I recently upgraded the chain and rear cassette (SRAM PG-830 and PC-830, respectively).

Now it seems like my crankset is acting up. My middle chainring is quite worn and with the new chain especially it tends to skip very easily on hills. Based on Marin's specs, the bike should have a Suntour NCX-410 crankset, and I've been told that I can't simply replace the chainrings on this part. I've done some reading (Todd Downs, Zinn books) about cranksets and bottom brackets while cross-referencing with Marin's specs. I think my bike has a sealed cartridge square taper bottom bracket, but I don't know anything about its size, etc.

I'm looking to this community for a recommendation on a good-quality but budget crankset with replaceable chainrings that will either work with my current bottom bracket (if it doesn't need to be replaced, how to tell?) or that would work with a modest bottom bracket purchase as well. I'm looking for the best value given that long-term cost of upkeep is a large factor in my upgrade/repair decisions.

Thanks in advance.
Unless your bottom bracket is giving you issues, you shouldn't need to replace it.  Sealed cartridge bottom brackets have quite long lifespans.

The link you provided indicates that the current crank is designed for a 113mm long spindle (that's the LL113 bit), which is a fairly common size.  My personal favorite square-taper crankset with replacable rings is the Sugino XD-350, which is also designed for a 113mm spindle.  It's basically a drop-in replacement for the cranks you have now.