I am about to buy my wife a DSLR for x-mas.

I am looking at the slightly used market (Ebay) because I was able to sell some stuff and have enough dough in my PayPal acct, to offset the cost pretty substantially.

She is not a photographer, but is very serious about her pictures (just ask my hard drive).

So I am leaning towards a higher-end entry level DSLR. Specifically looking at the Canon T1i, Sony Alpha 550, or maybe Nikon (but these are uncomfortably expensive).

So you can see I am hovering in the $500 to $600 range for a used camera and usually a single lense.

Any suggestions regarding these?

I'd say Nikon 1st then Canon.

The main reason in the enormous amount of compatible add-ons and lenses that are out there.

I used to be a 100% Sony consumer until the stuff I bought from them started falling apart and they wouldn't honor their warranties without a court order and an angry mob.
Seems they're more interested in busting teenagers for pirating music & software than they are in turning out a decent product.

PM Sebastes...he'll can give you a good run down of options...

I second the Sebastes and Big Stick recommendations. I love my D 200. As Sebastes said, "When I got my hands on the D 200 I knew this was the camera I had always wanted."

Stick and D200's won't fit the price range...

I know Sebastes talks up his D40x, you could easily find one of those with a kit lens for that range...

Mr Sebastes just mailed me a package with almost a dozen blow ups on heavy stock. Doug rocks.
Time to buy some frames.
ps Hey Doug....standing invite...
pps How many times have you invited a dude fishing and he:
Shows up early.
Has his own gear.
Gives you gas $ at the end of the day when you didn't ask for it.
Is a cool person to have around all day.
And then sends you nice pictures of your trip?
The list is short.

I see lots of D2100 bodies on ebay for around $600.