Minimal information would be the percentage gain/loss for the month and YTD for your account with a seperate box containing comparable measures for indexes that are likely to be a proxy for your account plus an indication of the yield on any cash in the account.
I've always liked the Morningstar percentile performance scale for mutual funds. It gives you an indication of relative performance. It's what I use in my columns because it is widely available information.
The problem with providing information is that there is little agreement on what is essential and useful among providers and there are great differences in the sophistication of the recipients. Some people are hungry for benchmarking information. Many others could care less. Their only concern is whether they have more, or less money at the end of a time period.
Scott