A while ago I found this list of GPS Chipsets Manufactures made in 2002 and another, longer list on a Canadian website. (The first lists on a table which is the best way to present this type of data). Not as comprehensive as the latter I'm listing the major brands below and I will add more IC's to the corresponding manufacturers as required:
Sirf (SirfstartIII), Qualcomm, Sony (Single-chip: CXD2951GA, Baseband: CXD2956AGL-1, Receiver: GXB5005/GXB5210), Fujitsu (MB87Q2040), Nemerix (NJ1030A Baseband processor, NJ1006A RF Front-End), Philips (SAA1575), Freescale* (i.250, i.300 platforms; MXC300, FS Oncore MG4100), STM (STA20576).
RF MicroDevices: Bluetooth/GPS Receiver solution RF8900 and RF8110 Software solution. SiGe GPS Receiver and Radio IC's.
Atmel: Antaris 4, Single-chip ATR0630 and ATR0635, RF Receiver ATR0601, Baseband ATR0621/22
Maxim: MAX2742, Single-Chip GPS receiver Front-End, MAX2674, standalone GPS receiver compatible to other baseband IC's.
u-Nav: GPS Receiver Baseband [uN1008, uN8031B]
Zarlink: GP2000, GPS Receiver Hardware Design [Application Notes, pdf]
A-GPS: Infineon [Hammerhead] PMB2520, Ceva Xpert-GPS 3000, GlobalLocate Marlin
*Motorola sold (Freescale?) GPS chipsets to Sirf.
Some companies offer only the Baseband IC, like Prolific's PL-6301 and Soc Solutions GPS-B3 and GPS-S3 that includes IP (Intelectual Property) blocks.
Most papers, including those from Sony, put at least two basic chips side by side: a baseband processor chip and the radio frequency receiver front-end.
This paragraph from the Maxim paper explains things in the clearest possible way:
GPS receivers on the ground pick up the signals and use the coded information to calculate a position on an earth coordinate system. A receiver determines position by calculating the time it takes for the radio signals transmitted from each satellite to reach the receiver.But I still can't quite understand what a "baseband" whatever is. Nemerix paper comes close to describe one: "GPS correlation is carried out by a correlator core optimized for high efficiency, low power correlation [...] delivering formatted navigation information (NMEA protocol) or as a flexibile GPS enabled microcontroller".
Multiplying the time by the speed of light determines how far the unit is from each of the satellites: Distance = Rate x Time. Time is determined using an ingenious code matching technique within the GPS receiver. The location of each satellite is encoded in its transmitted signal. With these data, the receiver can triangulate to calculate its location on Earth.
So in one word, it is software, IP.
I see things from the software-side more often and one can say that protocols are getting better defined. Hardware has its own set of issues about putting pieces, blocks together, at any level you want to talk about.
GPS World published "The Challenge of a Single Chip" back in 2001 which gives a good perspective on the current offers by describing what are the pieces needed for a GPS receiver.
One example of such combination was given recently by TearDown at EETimes: David Carey opens up a Navman iCN510 and describes its parts. A dedicated PDA it ends up being. An here is another tear down example.
In the same issue of EETimes, the eeProductCenter lists other GPS blocks from vendors including NEC, NavSync and u-blox AG among others.
Two other pointers here are the GPS Module by TRControl Solutions and the GPS Logger from Spark Fun Electronics.
To close, I also have to point out this paper[pdf] by Cello. Something that will help put cellular and location technologies in perspective at a similar hardware description level.