I tend to see this questions a lot. Either "What are the OM infotypes" or "What are the PA infotypes". It is always the popular questions among new users and even veterans to SAP. By looking at the infotypes number, it seems like there is no ryhme or reason how they are group, but there actually is.
0000 - 0999 is PA related infotypes
1000 - 1999 is OM/PD related infotypes
2000 - 2999 is Time Management
4000 - 4999 is Recruitment
5000 - 5999 is Erecruitment & E learning
9000 - 9999 is customer specific infotypes
To see a list of all OM related infotypes, you could use transaction code OOIT or table T778T.
On help.sap.com, they do offer a pretty extensive list and description on all of their infotypes. You could check it out @ http://help.sap.com/printdocu/core/Print46c/en/data/pdf/HRINF/HRINF.pdf