There is no limit to the amount that an individual can contribute to any charity.  The real question is:  How much can I give without causing the recipient to become a private foundation instead of a public charity?
The issue of “tipping” a public charity into private foundation status has been around for a long time, even though very few charities actually do tip to becoming private foundations.  If your charity is dependent on broad-based public support from contributions or fees for its public charity status, you can probably give about two-thirds of its support over a 5-year moving average.  The basic rules under sections 509(a)(1) and 509(a)(2) of the Tax Code basically define a public charity as a charity that receives one-third of its total support from the proper public sources.  (See Ready Reference Page: “Calculating Public Support Percentage” There are a number of wrinkles on what and how much can be counted as “public.”) Most charities are not particularly close to the line.
Occasionally a founder puts so much of his or her own money into the enterprise that the fraction becomes a problem.  In those cases, because additional contributions from the founder are of limited or no value and contributions from other public charities are included fully in the numerator of the fraction, the founder may give the money to a donor advised fund (which is sponsored by a public charity) and recommend a grant from the donor advised fund (i.e. from the public charity) to the founder’s charity that is close to the line.  The public support percentage is immediately increased.
That is legal today, but the IRS questions whether it is appropriate and most of the legislation proposed to regulate donor advised funds would require that DAF funding be traced back and attributed to the original donor or adviser, eliminating the effectiveness of the technique.
If your organization is defined by section 509(a)(1) as a public charity because of its activity and not because of its revenue stream, like a school, a hospital or your church, you don’t have to worry about where the support comes from.  Public charity status for those organizations is not dependent on the source of support.  As I said, if your charity is a church, you can give whatever you want and are able to give.