Google likes sites that take part in the “egalitarian web”, so don’t fear linking to other useful sites and don’t listen to scare-mongers who will tell you that you’re “leaking link juice”.
While we are on the topic, “link juice” has to be one of the worst metaphors in the history of the web. I’d rather it were “Tiger Tokens” or anything else that didn’t sound like it would ruin your best shirt if you got it on you.
Don’t be afraid to link out to other sites that complement yours or would be relevant to your readers/visitors. Nobody in their right mind is going to link to a direct competitor, but that doesn’t mean that you can’t provide some useful and informative links to other sites.