The Greek New Testament from United Bible Society now in 4th edition
Novum Testamentum Graece et Latine (same as this but together with Latin Vulgate)
The difference between the one offered by UBS and this one is that this has more footnotes on differences between manuscripts. In this newest edition, the actual textual decisions between the two are the same. The UBS is better for those who want to use the text for translation, and this one is better for those who are interested in studying textual critical issues.
Also keep in mind there are many interlinear Bibles out there that are probably better for those whose knowledge of Greek is limited. Take care, however, to distinguish between those which are based on Stephen's 1550 Textus Receptus and those which give a complete apparatus for comparing many manuscripts. Most biblical scholars feel the Textus Receptus was flawed in many ways.
1. A different font is used for the text itself. Not just a different font, but a repellently ugly font that has not much resemblance to any font with which a quality edition of a Greek text has ever been published before. Yes, ever. The geniuses at the United Bible Societies are the first people (going back to Erasmus' publication of a NT edition in 1516) who thought that a hideous, spindly, faux-italic computer font would be a better choice than ANY of the established Greek fonts that heretofore have been used in the printing of ancient texts. I hope you'll forgive my emotion on this point, but, as a scholar of (Classical) Greek with a library full of Greek texts published by Oxford, Teubner, etc., I am just flabbergasted to see such disregard for tradition as this. The UBS4 font choice is analogous to printing an English Bible in one of those goofy "Calypso" or "Horror Movie" fonts that come with Windows. The UBS3 (1975) and its corrected edition (1983) are both presented in an attractive, standard typeface that would be suitable for a printed edition of any ancient text.
(As an aside: the Nestle-Aland "Novum Testamentum Graece," in some ways the more conventional current scholarly edition of the NT, is also marred by its odd, cramped way of indicating textual variations. Again, Nestle and Aland's innovation of intruding a million squiggles, squares, circles, etc., into a text, is not an improvement over the traditional apparatus criticus--it's just an awkward space-saver. This is a major reason why anyone who wants a clean, accurate, up-to-date Greek text of the NT may want to choose UBS3 over Nestle-Aland.)
2. The other difference is in the selection and presentation of material in the critical apparatus. Here, I'm sure there were sound scholarly reasons. Note that in the UBS Greek Bibles (as opposed to the Nestle-Aland "Novum Testamentum Graece") the point of the apparatus criticus is not to present the larger manuscript tradition and variations synoptically, but to focus in on only those textual variations that might affect the translation of a passage. For these passages, the apparatus indicates a committee's judgment (indicated with a letter scale: A, B, C, D) on the different possible readings and punctuations. Unfortunately, here too the revisions are not definitely an improvement. As Edward Hobbs, a distinguished Professor of Religion at Wellesley College, wrote on a popular Biblical Greek email list, "I also prefer UBS3 or UBS3c, since the evaluations have not undergone the 'grade-inflation' of UBS4. (Slightly different method used to describe the A,B,C,D grades, but the committee membership changed over the years to a more-traditional-in-some-ways and more-clones-of-Aland-in-other-ways group.)" The upshot of this is, the range of information and opinion you get from the apparatus in UBS3 is not obsolete and not inferior to what UBS4 offers.