It all depends on what kind of price point you can afford.
For pH, Mettler Toledo has some in situ process sensors (triclamp connection) with associated transmitters. Typically giving you a 4-20ma output with which you may convert to 1-5v as BrunDog mentioned (250 ohm 0.1% tolerance or better, and I use a 1N4733 Zener diode and current limiting resistor to protect the microcontroller input in case of wiring failure). I have the Mettler Toledo 2100E.
For Gravity, Endress-Hauser and Micro Motion are probably the two most popular Coriolis effect flow meters in the industrial/pharmaceutical/biologic industries. As they are meant to be flow meters, the measurement technology also calculates the specific gravity of the fluid flowing (in addition to temperature). These sensors are very expensive when new, but can be picked up for "reasonably inexpensive" on eBay, or second hand. You'll want to be careful which you choose, and what options they have, as some don't have outputs for all of the measurement variables (temp, flow rate, specific gravity...). In my research, the Micro Motion 2700 transmitter has multiple outputs for the variables, and Endress-Hauser 63 or 83 series transmitters have multiple outputs. You also need to keep in mind that these sensors aren't small, and sometimes need to be "clocked" in the correct orientation for flow stability and drainage. The most expensive types of these have straight tube or tubes instead of U shaped bends, which can be mounted in just about any orientation. Ones with U shaped bends "should" be mounted vertically for absolute drainage. Regardless of type, the same 4-20ma output is available, and some have HART protocol, RS-485 or RS-232.
Cheers!