The Zoom H4N was awful & the Tascam DR100 was a little better (did have quite a low recording volume).
I eventually went for the Marantz PMD661 - it was a little overboard, as i had a proper mic & a field mixer, but as a back up its excellent.
The problem is that al lot of these recorders just don't have great onboard mics etc.., so they're noisy crap.
However, if you get a secondhand mic & plug that in, then they can turn an H4N or DR100 into a butterfly!
XLR inputs essential, as is Phantom Power, on a recorder.
Sennheiser K3-U/ME-80 - an old, low budget film mic, which sometimes comes with all 3 mic extensions (ME-80, ME-40 & ME20) & can run off a battery or phantom - under £100.
This was the best review site i found when i was looking for a recorder:
http://www.wingfieldaudio.com/portable-recorder-reviews.html
But as with all things you can go really nuts or just slowly build up.
If you're budget minded - you can pick up a small used 2 channel mixer, an old mic & plug it all into a small recorder - will all fit into a small bag which you have over your shoulder & the mic can be shotgun handheld or fixed to your camera. The quality will be sooo much better than onboard mics. All said & done £500 or less - if you're careful/patient looking for a bargin.