mandolincafe.com is a great resource. I bought a custom A-style mandolin and a used flat-top mandolin from their classifieds.
This question is totally dependent on budget, and also on the person you are buying the gift for. I can tell you that you want a solid wood mandolin if you can afford it. Most budget mandolins have "laminated" (plywood) back and sides.
Is the recipient already a musician? Do they really want to learn to play or do they just like the "pretty" mandolins (F style, the one with the "curl"?) What type of music do they want to play?
If they really want to learn the instrument, go to the top of your budget and pay for materials, not style. Eastman and Kentucky make reasonably priced entry and intermediate level instruments. Eastman 505 and Kentucky KM-150 are sort of the border between entry level and intermediate. Here is an Eastman 605 used on mandolin cafe that would be a great value, even has a good pickup.
FS Eastman MD605 Mandolin - $600 - Mandolin CafeAnother way to go is flat top. I enjoy playing my Flatiron flat top as much or more as my custom A style. See below for example.
Kentucky KM-120 Army-Navy Special Mandolin - Saga MusicWhatever you do, get a good setup on it, get the action as low as you can for a beginner. Have them make it playable as possible.