A Scanner for slides is the only way to get a perfect work. The Epson suggested by sig is perfect.
I have an old Nikon scanner with USB connection which is no more comtible with MAC. I still use it connected to Win XP running on my Mac under Parallel.
The problem with a slide scanner is the time needed, for a good job it takes about 2-3 minutes for each slide (clean - load - focus check - settings to improve colors or remove scratrches - actual scanning - save).
There are also a scanners which load slides automatically: very expensive, you have less work bur the time needed is similar and you cannot be sure about focusing and adjustments.
If the slides are really many (I have 4 - 5.000) in my opinion the best way is to start with a 2 steps approach.
I did as follows:
Leave the slides loaded in their rail holders. Each rail has a number, and each slide its position in the rail.
First quick catalog done taking pictures of the slide projected on a screen. No need for great quality camera: put it on a tripod and go. You will use the pictures only as a catalog, they will be to bas for any use. Few hours to get thousand of jpg files. Very usefull if you can use a camera which lets you set the first 3-4 digits in the filename in a way which will refer to the slide rail number.
Second step. Take a slide projector (your own or an old one from eBay). Change the lamp with a Led. You have to check the voltage. Mine was 24 volts: I used 2 Led each 12V in serial connection, each about 1 Watt. Prefer the flat round type with many leds on it. Put an opaline white glass or plastic in front of the led lamp. Remove the projector lens and with a good SRL with extension tubes on a tripod take pictures of the slides. You will need probably a long lens because it will be difficoult to go near to the slide which is inside the projector. I used a Leica projector and a Pentax 20D with a zoom lens at 140 mm on 2 extension tubes. It is important to have auto extension tubes but without autofocus. The light let me use 1/100 at F 8 - 9,5. The worst problem is you need to revers each slide in the rail, upside down - vertical shots need to be put 90 degrees and the emulsion should go in the direction of the lamp not to the lens like it is during projection. It is a little work but you can quicly take picture of one slide in 5 seconds. Change slides advanceing manually the rail in the projector , check focus and shoot. It takes few hours for 1.000 slides. Focus at full aperture and shott at about 8 - 11 as F stop to get anough depth of focus to compensate.
Use raw. You will be able to adjust the pictures in your Aperture or Photoshot later. I did some test with a setting of the white on the empty projector but at the end I left the camera decide and eventually adjusted later on the raw file.
You end with pictures which can be used for some internet use or to be sent to parent and friends.
With this catalog you can go to the slide and take a scanner only if you need it for a print or a very good result.