There's a three-month plan and a six-month plan, and they come with a guarantee: If, after three months of paid membership and communicating with at least five members, you're not satisfied, eHarmony will refund your money. While you can review the profiles of your prospective matches for free, you'll need to pay to unlock the full features of the service.
EHarmony was one of the pioneers among online dating site options, and - while I haven't personally used this one - we all remember the pitch for online daters, thanks to years of TV commercials: The service matches couples based on "29 dimensions" of compatibility and interests (as determined by a thorough relationship questionnaire and personality test).