Avoiding a lengthy wait for a table has long been incentive enough for many diners to make advance reservations. Now, new standalone reservation web sites offer a few more reasons to plan ahead, including discounts, extra credit-card rebates and reward points.

Many of such sites cater specifically to city dwellers. VillageVines.com, which offers discounts of up to 30% at partner restaurants in exchange for a $10 fee per reservation, began offering deals Wednesday in Los Angeles, San Francisco and Chicago. The site was already operating in New York and Washington, D.C., where it offered discounts like 30% off the total bill at foodie havens Le Cirque, Vidalia and Fatty Crab.

Another reservation site, DinnerBroker.com, aims to re-launch later this month with an offer to reimburse American Express cardholders as much as 15% of the cost of their meal. Diners will receive a statement credit for making reservations through the free site to dine at partner restaurants and paying with their registered Amex.

Such sites can be a double-edged sword for restaurants, says Aaron Allen, a restaurant consultant. The marketing message is more targeted than it is on a billboard or in newspaper ad, but chasing discount seekers with big discounts can be dangerous for businesses that offer menus with different (and mostly slim) profit margins on each dish. It s a suicide pact of these restaurants dragging prices down, he says. Sooner or later, the venue must scale back deals and lure more diners willing to pay full price.

For their part, consumers focused on reservation rewards may lose the chance for even better deals. I don t think the reservation portion is key, says Joan Simon, the owner of Reservations Tonight, a restaurant concierge based in San Francisco. Group-buying sites like Groupon.com routinely offer discounts of 50% or more on restaurant vouchers, while Blackboard Eats rewards subscribers with texted discounts of 30% to present to a server tableside, she says.

Here s how to make sure you ll benefit when booking online:

Eat early

OpenTable.com regularly awards diners 100 points per free reservation, but raises that to 1,000 points for tables booked at select times. (At Spago in Las Vegas, that s between 5:30 and 9 p.m. daily.) Earning 2,000 points earns a $20 dining certificate that can be used at any partner restaurant. DinnerBroker.com also offers bigger discounts for dining at less popular times.

Assess available deals

Before booking, check for other specials and discounts at the restaurant to make sure you aren t passing up a better deal, Simon says. A party of two who want to try Le Cirque, for example, would save $101 on the $185 chef s menu with wine pairings by spending $10 to book through VillageVines.com. But the restaurant also currently offers a $35 three-course dinner that could also be a good fit (and stacks with OpenTable.com rewards).

Book in advance

Reservation sites let eateries control the number of tables that can take advantage of a booking discount on a given day. Reserve a table as soon as possible for a better chance at the deal.

Watch for dining restrictions

Restaurants may limit offers to certain menus, Allen says. Read the fine print to make sure you won t be forced into a special menu or end up paying full price for a bottle of wine. DinnerBroker.com requires users to pay with a registered American Express card to get their deal.

Check with the restaurant

Some offer their own deals for booking directly online, such as New York s Indigo Indian Bistro, which will knock 15% off the bill.