My family and I are looking for two or three great restaurants in Boston for a special occassion weekend. Price doesn't really matter and neither does cuisine type.
We've been to Sage before and are thinking of returning for one of the nights. Any suggestions?

well, there are so many possibilities, it seems difficult to choose without narrowing it down somehow...by location, or cuisine type, or atmosphere?

but what the heck, I'll name some of my favorites anyways:
Radius, Excelsior, Via Matta, Hammersley's Bistro, L'Espalier

All of these will run you a pretty penny. But I've had consistantly great food at all of them.

French, Italian or American

There's a wonderful new tapas restaurant on Washington Street in the South End.
All the above restos are very good, I'll add Mistral, Clio. Oleana.

For special occasions, L'Espalier gets my vote.

let me add some details to my post then.

L'Espalie is french, and very expensive. Its in house on Newbury street, so there are several small rooms as dining rooms, which makes it cozy and intimate. It's a wonderful place for a romantic evening.

Radius is on the edge of the financial district. It's contemporary American, and is often rated the best restaurant in Boston. It's a cool looking room, but a little noisy and not great ambience. But the food and service have been great. I've been 4 or 5 times, and never been disappointed.

Via Matta is run by the same owners as Radius. Its not quite as pricey as the first 2. Its Italian. I think the food here is wonderful. Not overly fussy, or piled with lots of ingredients. Its fairly straightforward. they do an excellent tasting menu, I like going with a group and then getting to try many things.

Hammersley's Bistro is french, and located in the South End. Its been around for a long time, and is one of the most consistantly good restaurants I know of. Last time I went, I had pan roasted lobster with truffles and it was awesome. The roasted chicken there is a a classic bistro dish, and they are famous for it.

Excelsior is another contemporary American restaurant. Lydia Shire owns it, and she is well known for creative contemporary cuisine. This is not as 'creative' (meaning weird) as Biba was. but the food is excellent, and you can see things that are quite different.

The ones Cigale mentions are all good choices too. I haven't been to them all, but I have been to Oleana, which is in Cambridge and I was very impressed. It was upscale middle eastern, which means it had some very different sorts of dishes. The dining room was kind of small and crowded though. that detracted from the ambiance a bit.

China, go in the summer. Dining in the garden is delightful but go early no reservations for outside unless there has been a change. We eat at the bar when not in summer.

Shire has also taken over the venerable Loc-Ober's.
Also want to mention Upstairs in the Square in Harvard Sq, but I do miss their old location where you could dine al fresco.

I love all the restaurants mentioned, esp China Cat's list, to which I would also add Spire (Boston) and Rialto (Cambridge) which often has great jazz in the Regatta for after, and being in and around Harv sq can be fun. If you want something in North end besides Sage (which I also love) , we also enjoy Rabia's. We also had a great meal at Torch and Charles St is a nice street to mill around, but it was a year ago.... you can also check out on www.opentable.com for the dates you will be here and while every restaurant isn't a partner with this site, you can see what is available certain nights and many have links to the restaurant menus (Sage I have booked thru this site as well as Rialto) and it saves you lots of phone calls if you are coming from a distance.

and China Cat I can taste that chicken at Hammersleys', I need to try something different there sometime, but I can't seem to bring myself to do it it's just so delicious.