Via AIDSMap -- just confirming what was already widely suspected:

The two sexually transmitted infections most strongly associated with HIV acquisition in gay and bisexual men are anal warts and anal gonorrhea, Australian researchers report in the online edition of the Journal of Acquired Immune Deficiency Syndromes.

Herpes infections did not emerge as significant in this study, but men with warts were three times more likely to acquire HIV, and men with gonorrhea were seven times as likely. The authors suggest that more frequent screening for anal sexually transmitted infections in gay men should be investigated as a means of HIV prevention.

Interesting that herpes was not correlated. If you're unaware, STIs like gonorrhea can increase risk for transmission for a number of reasons. In cases where STIs cause lesions (like syphilis or HPV), these sites become more vulnerable for transmission. Also, in general, it seems that co-infection with STIs can dramatically increase your HIV viral load, thus making it easier to transmit the virus. In this study, it seems that these infections are also highly correlated with unprotected anal intercourse -- thus there's a reason men with these infections were more likely to acquire HIV.