My wife totaled our 99 Volvo S70 this morning (not her fault). Everyone is fine, but the car is toast.

I have not bought a car in a while.

I am probably not going to buy a NEW car. Probably a certified used car. Any suggestions on a safe sedan that is reliable and not too expensive. I'm thinking 2002 and under $20k.

Any negotiating tips?
Any good sites that list real values?
Anything else I need to know?

Honda Accord.

Lexus ES330.  Nice car, top-line safety systems and Lexus Pre-Owned program rates very high in the Customer Satisfaction scores for those type of programs.

Quoted: Lexus ES330.  Nice car, top-line safety systems and Lexus Pre-Owned program rates very high in the Customer Satisfaction scores for those type of programs.

Can I pick up one of those for less than $20k?

I've heard real good things about the Toyota Avalon.  Many say the quality is on par with a lexus but still carries a toyota badge.   Nissan Maxima's are great cars as well.  260hp, great stereo and sporty looking.  Honda Accord and Toyota Camry,  two cars that you can't go wrong with.  

you know what you want, so just go out and get it.  I won't give you any tired Chevy vs Ford vs Toyota arguments.  My best tricks for buying used vehicles is as follows:  (BTW, I've bought A LOT of used vehicles and am IMHO a rather accomplished shade tree mechanic.  It took me quite a few lemons to develop this list!)

1)  Always run a Carfax check.

2)  Always have it checked out with a reputable mechanic, or, if you know what you're doing, do a
     thorough check yourself.

3)  Check the preprogrammed radio stations.  It sounds stupid, but a car owner that listens to    
     loud rock/rowdy country usually doesn't treat the vehicle well.  Talk radio is usually a safe bet.

4)  Really inspect the interior.  A car owner that doesn't take care of the interior isn't going to take
     care of anything under the hood either.

5)  If buying a certified used vehicle, have the dealer run the VIN for periodic maintenance.

6)  Don't be afraid to walk away from a vehicle if something isn't right.  

7)  Don't be afraid to haggle.  You don't have a lot of room to haggle at a used car lot, but with
     private sellers, if you do your research and know what the dealers will offer for trade value
     and offer a FAIR price, you'll be surprised at what you can get for your money.

8)   DO NOT SPEND MORE THAN YOU ORIGINALLY INTEND TO.  If you plan on financing, get  
      your loan beforehand (if possible) and put 10% aside for some repairs.
      You're probably going to have to drop some $$ for minor repairs no matter what.  Nobody sells
      a perfectly good car without a reason.  If you don't use the set aside $$ for repairs, give it
      back to the bank as an early payment.  

There are obviously exceptions to every rule, and you're not guaranteed a fantastic, trouble free car using my techniques, but they've worked for me so far.  My current primary vehicles are both high milage second hand--99 Chevy Silverado (155K miles) and a 99 Ford Explorer 4x4 (142K miles).  Both look new, smell new, run like new and I paid...$3200 for the Chevy, $5800 for the Ford.  

BTW, if you ever want to buy a chicken in Tijuana, let me know

Buy ANYTHING Toyota and forget about it!!!!

I only buy American, but that's just me.