There are nearly endless benchmarks (see a short list of relevance at Benchmark Programs and Reports on the Top500 site) and it may need a bit of work to understand each benchmark's implications (see Benchmark Tutorial, in IEEE Micro 1989, or An Overview of Common Benchmarks in Computer 12/1990). Benchmarking will always give only a rough estimation, so all numbers should be taken with a serious amount of salt.
Having said that, one of the longest running measurements, the Whetstone Benchmark, is quite useful for us, as it's been around since 1972. Its details were described in an article in 1976 Computer Journal. Its result is given in so called Whetstone Instructions Per Second, usually noted as KiloWIPS or MegaWIPS.
Originally developed in ALGOL60 it has been ported to next to all languages available and many computers. This was possible as the benchmark isn't defined as a specific source code (like with SPEC), but a series of (FP) operations. So, to some extent, it also relies on programming skills as well as the compiler used. Alas due to its simple nature, programmers' skills will only show up as long as the compiler is rather bad in supporting a (new) machine.
As with every benchmark, it also measures memory access, control structures, etc., not only FP instructions. But translation is rather well defined, so with detailed numbers, WIPS can be translated into FLOPS. Or just used as they are for the sake of simplicity.
Some examples for common machines are:
MWIPS Machine Environment
0.0027 Apple II Applesoft
0.0188 PDP 11/20 Fortran
0.0852 80286/87 Fortran
0.74 VAX 11/780 Fortran, No FPU
1.02 VAX 11/780 Fortran
2.4 SUN 3/160 Fortran 68020/881@16 MHz
All values are taken from the Whetstone Benchmark History and Results, written by Roy Longbottom who was involved with application of Whetstone almost since the beginning. It provides not only much information about the development, but also quite extensive lists of machines, focusing on scientific usage. His site includes quite a lot more information about benchmarks than just Whetstone.
But there are many other sites/lists around the web, so a search may help to find values for the machines you are searching for. Or just go ahead and implement it yourself - it's really just a few (hundred) lines of code (some FORTRAN required).