If you are going to calibrate two monitors seperately, then Spyder 3 Pro will do, or Colormunki Display, or Colormunki Photo, as well as some of the x-rite I1 products - these are aimed more at the professionals though. CM Photo will also help in calibrating your printer. If you need/want a studio match for the two monitors, then you will need Spyder 3 Elite. The "studio match" tries to match as closely as possible the color gamut of both monitors. I have Spyder 3 Elite and it works pretty well for me. I also have Colormunki Photo, but I am currently only using it for printer calibration as it will not do a studio match. It could still be a little tricky, because the U2410 is an H-IPS monitor and the ST2310 is a TN panel. I have the ST2310 and an ASUS PA246Q wide gamut, IPS monitor. The Spyder 3 Elite will calibrate them both very well individually, but the studio match currently leaves a bit to be desired - they are completely different monitor technologies and I suspect this has a bit to do with the less than excellent match I sometimes get. Plan to add another monitor to replace the ST2310 in the new year - will probably get another ASUS PA246Q. Before I got the ASUS monitor, I had 2 TN monitors and the "studio match" process with them worked quite well. Hope this helps.
Cheers,
WesternGuy