Small libc for embedded systems

PDCLib might fit your needs. It's still incomplete [broken link], though, and probably in need of a lot more real-world testing. Its author goes by DevSolar here on SO.

update 2012-11-01: As of 2012-08-14, development has been taken over by Owen Shepherd, complete with a new homepage and bitbucket repository [broken link, use this one].

update 2015-10-31: The dedicated website seems to be dead, but the code can still be found on bitbucket. The last commit to that repository happened 2014-11-24.

update 2016-07-12: The website is back up, and DevSolar started committing again on 2016-03-01.

I use newlib on my Cortex_M3 with 32kB RAM, and to eliminate the malloc() you can use siprintf() or sniprintf().

Pro: No more calls to malloc().

Con: It does not suport formatting float and double, and is not really portable this way.