Which IC can support LED debug of logical circuits?
If your worried about altering the state of a circuit, then use a comparator or op amp to drive the LED. This is called impedance buffering. The input impedance is usually in the uA's or less even down to the pA's (you can find out by looking at the input bias current in the datasheet, this is how much current leaks into the input ports of the amplifier). So that is like adding a resistor to the output of your gate with a resistance of 1MΩ or higher. For a gate that is sourcing 10's of mA it won't even notice.

For digital circuits even using gates to buffer can be quite common, make sure the gate can source enough current for the LED (check the datasheets for both) and make sure you add series resistance between the LED and whatever your using to drive it with.