HP are the most beginner-friendly choice.
After HP, other hardware to check that will probably (but not definitely) work are those included in the SANE scanner drivers list and in the Gutenprint printer drivers list. See the following two links for details:
http://www.sane-project.org/sane-backends.html#SCANNERShttp://gimp-print.sourceforge.net/p_Sup ... inters.phpI use Canon MFPs successfully in both Gentoo and SL, but would not recommend them for newcomers to either distribution, as Canon MFPs can be difficult to set up in Gentoo/SL (and not every Canon model works in Gentoo/SL), although Canon do provide packages for Linux distributions that use .deb and .rpm packages.