wolfchid pretty much hit the nail on the head.

If you're a pro, your time is probably best spent on the bike.
If you're someone who enjoys cycling and doesn't want to look like crap, hit the gym, it's not going to slow you down.

If you have a gym membership, I'd reccommend bench pressing, rows, pullups, and the overhead press. Those should be the main four lifts. Then you can supplement them with things like curls, pulldowns, pushdowns, etc.