- 70 citations/month, Five-Year WMAP Observations: Cosmological Interpretation, by WMAP Collaboration, arXiv:0803.0547

The absolute leader, even though they were hardly the news last year: one needs very large telescopes to tell the 5-year results from the 3-year ones. Nevertheless, quite deservedly, they keep receiving the credit for turning cosmology into a precision science.(Actually, there should be two more WMAP clones in this list: arXiv:0803.0586 and arXiv:0803.0732 who have received 32 and 22 citations/month respectively, but these two got disqualified for obscuring the view.) - 26 citations/month, N=6 superconformal Chern-Simons-matter theories, M2-branes and their gravity duals, by Aharony, Bergman, Jafferis, Maldacena, arXiv:0806.1218.

So this is the most cited 2008 theory paper... It constructs novel gravity duals that employ the notion of M2 branes. I have no idea how important this is. Go ask Jacques, who has a post on the Bagger-Lambert construction of M2 branes, and another one that includes a brief comment on the Aharony et al. paper. - 26 citations/month, Observation of an anomalous positron abundance in the cosmic radiation, by PAMELA collaboration, arXiv:0810.4995.

PAMELA was definitely the star of the last summer: the paparazzi affair was more widely discussed than Britney Spears' new look. On top of that, PAMELA's observation of a cosmic-ray positron excess in the energy range 10-100 GeV was readily interpreted as an indirect signature of dark matter annihilation/decay. This spawned a whole lot of theoretical activity, including the paper below. - 19 citations/month, A Theory of Dark Matter, by Arkani-Hamed, Finkbeiner, Slatyer, Weiner, arXiv:0810.0713.

Once again Nima set the direction. The paper proposes a model that explains the PAMELA excess and a few other mysterious astrophysical results. The crucial feature is the hidden sector hosting dark photons (cool name) with GeV scale masses. - 16 citations/month, Superconformal Chern-Simons Theories and AdS(4)/CFT(3) Correspondence, by Benna, Klebanov, Klose, Smedback, arXiv:0806.1519.

It is a new development related to the Aharony et al (number 2 on this list) who in turn is a new development related to the Baggert-Lambert construction of M2 branes... - 13 citations/month, Averages of b-hadron and c-hadron Properties at the End of 2007, By Heavy Flavor Averaging Group, arXiv:0808.1297

That must be very important, even if Heavy Flavor Averaging Group sounds a bit ominously. - 12 citations/month, M2 to D2 revisited, by Ho, Imamura, Matsuo, arXiv:0805.1202.

It's a pity there is no R-branes yet in string theory; R2-D2 would make an even better title. - 12 citations/month, M2-branes on M-folds, by Distler, Mukhi, Papageorgakis, Van Raamsdonk, arXiv:0804.1256I'm afraid I have run out of jokes on M2 branes. Given that I have no intelligent comments in store, I'll just skip to the next one.
- 11 citations/month, Three-flavour neutrino oscillation update, by Schwetz, Tortola, Valle, arXiv:0808.2016.

Nobody expects the Spanish Inquisition...people out there are still working on neutrinos...

Congratulations to Thomas - the only CERN theorist (now ex-) who has made it to this ranking. - 11 citations/month, Bagger-Lambert Theory for General Lie Algebras, by Gomis, Milanesi, Russo, arXiv:0805.1012.

Heeeelp....

Update: It was pointed out to me that R2D2 is already on ArXiv :-/