Currently I am in a 25% Tax Bracket and I plan to sell stock and will incurr a capital gain of $200,000. Will this affect my marginal tax bracket? I know I will pay capital gains taxes on the $200,000 but will the $200,000 be added to my AGI and affect my marginal bracket? (i.e. bump me up into the 33% bracket)
It will definitely be added to your AGI, but not necessarily bump your ordinary income tax bracket.
You will have to use the Capital Gains Computation worksheet (that uses the general Tax Computation Worksheet) to figure out your tax liability. You might also be subject to the AMT. See the instructions to form 1040, line 44 (page 38) and line 45.