Is there a way to see reputation change over a specific period of time? For example, say I want a solid number on how much reputation I've gained/lost in the last year. Is there a simple way to get this information?
Well, if you're only looking for how much reputation you've gained in the past week, month, quarter, or year, you can use the Users page. Just type in your username and then select an option from the menu and it will show you the amount of reputation you've earned in that period and even the top three tags you participated in:
Edit: I just realized that these wouldn't be exactly what you'd want, as they're not as straight-forward as they appear. The year tab doesn't look at the "past 365 days" as you'd expect, but rather everything you've done this year... They go more as follows:
I suppose if you want to look at a time period of 365 days instead, you'd have to subtract the values from your SE reputation graph...
If you want to find the amount you gained in a specific period between some date #1 and some date #2 (not necessarily today), you can visit the reputation tab on your Stack Exchange profile and find date #1 on the graph somewhere and date #2 on the graph somewhere and just subtract the values.
You can see a list of every single event here:
Or you can see how you stack up compared to others here:
You can get to the reputation leagues by going to your profile summary, clicking on the "Top 38% overall" link next to the Reputation header, and then changing the time frame.