We have the Little Tikes Adjust 'n Draw Table ($40):
http://www.littletikes.com/toys/toys-detail.aspx?Product_ID=3200&Ntt=draw&N=26&Ntk=Product Search

I did an extensive search for the perfect play table and settled on this one. My toddler has used it every day since we bought it a few months ago. It can be used for doing artwork, having tea parties, Lego building sessions, meals, etc. I like the way it converts to an easel too. Also, it's easy to clean and move from room to room.

I think it all depends on how it will be used.

Is it primarily for trains and building blocks, activities that are usually done standing or kneeling, or for drawing and eating, which may require chairs?

How many children must it accommodate?

Does it need to serve any additional purpose (e.g. storage or even use as an adult coffee table)?

Does the tabletop need to be cleared for storage to be accessed?

I got one for $20 from Ikea that came with two chairs. I didn't have a good idea of how my daughter would want to play (like listed above) so decided to be cheap at first. Right now she likes to sit in a chair and play with her doll house or do play doh. But it is starting to seem a bit small, so I think we'll be upgrading soon. What is also hard is that they come at different heights--I wanted the chairs to be useful right away and with many sets they are too high.

NCB: You're right about the height issue. We're looking for a play table that our little one can stand at and play, rather than table chair set he has to sit at. He's still too young to sit in a chair for any real amount of time.

MamaChilanga: Just one child; no other function necessary; and like I said, for standing play.

We have the ducduc table and LOVE it - it works for everything from a train table to a chalk drawing board, and is the primary large storage (the rolling drawer underneath) in our room. That said, it functions more as a coffee/center of the room table than a table/chairs set, for which we purchased another inexpensive set that is pushed in the corner w/ two small chairs.

Community Playthings sells maple tables that adjust in height for differently-sized chairs as kids get bigger, and can also be tilted like easels. They seem to be at the lower end of the price range here, and they'd probably be useful for a lot longer.

It really depends on what your child will be using the table for. Ours likes to use crayons, markers, and playdoh on the table so we bought the Mammut table and chairs from Ikea. Table was about $35 and the chairs are $15 a piece. There hasn't been anything on that table that I haven't been able to scrub off yet. It's cute in our playroom especially for that price.

I love the DucDuc table, but it doesn't accommodate the Thomas train board; you'd have to have it custom-sized for that.

As MamaChilanga says, you would also need a table at a different height for drawing etc. We got a great one at IKEA for $30 -- forget the name, but it is a white trestle table. After looking and looking and looking, it really was my favourite. Of course, they have discontinued it! So now I kick myself for not having bought 2 of them (they are great as a kids table at dinner parties and birthday parties...)

I just saw a great one at Costco of all places. It's not listed on line though. It was circular with a hole in the middle... bent plywood looking (I didn't inspect it closely) with two chairs. It was so cute and inexpensive that I actually thought I should get it even though I don't have nay kids yet!

As a child my parents found a taller table second hand and chopped the legs in half. It was a big table and we used it for years.