My recommendations depend on your budget and what your intended use is for tubular tires, so I'm going to break them up based on usage. These are all tires I have a lot of experience with and trust. There are also good tires made by Dugast, FMB, Hutchinson, Vredestein, Scwalbe and others, but I haven't used them myself and don't know enough about them to make recommendations.
If you intend to use tubulars on race day only, never for training:
-Conti Competition Expensive but very good feel and traction, not the lightest but light enough for racing.
-Vittoria Corsa Evo CX Slightly less expensive, lighter weight, very supple, not as durable or puncture resistant as the Conti's.
-Conti Gran Prix 4000 A little less expensive than the Competition, different tread pattern, otherwise similar.
-Tufo S3 Light 215gr Very light, very good puncture resistance, tubeless so you can pre-install Tufo sealant and eliminate most flats, always true and round, not very supple and in testing has not had the lowest rolling resistance.
-Conti Sprinter Middle of the price range, very supple, great cornering grip, these are what I'd use for American-style criterium racing.
If you want a tubular for both training and racing:
-Tufo S33 Special (not the Pro) Very durable and puncture resistant, tubeless so you can pre-install Tufo sealant and eliminate most flats, reasonable price, always true and round, not very supple and in testing has not had the lowest rolling resistance.
-Conti Sprinter Gatorskin Same as the Sprinter above, but heavier and tougher due to the Gatorskin casing, not as supple, better puncture resistance.
-Vittoria Corsa CR Cheap but nice, 220TPI casing, supple, decent puncture resistance, not light.
My personal choice for all of my road riding, training or racing, is the Tufo S3 Light 215gr. It's probably the lightest of the tires listed above, and what you lose in rolling resistance is made up for by almost never having a flat. Just make sure you buy a small tube of the Tufo tire sealant and squeeze about 1/3 of it into each tire before gluing them on and you'll never get flats from anything smaller than a framing nail. If money is no object, the Dugast and FMB tub's are generally known as the cream of the crop, but I'd save those for race day only.