Before I recommend a font, I am goint to recomment this website: wordmark.it
No, it is not for you to download fonts, in this website you write a word or a phrase and it shows that word or phrase in all the fonts you have installed in your computer. It is GREAT.
Now, the fonts I use are mostly Comic Book and Candara. Comic Book for ballons, Candara for "subtitles", I like how the numbers look with Candara.
Here is the use of "Comic Book" on End.
And here is how I would use Candara.
There were other fonts I like, but I do my webcomics in both english and portuguese, and there are some beautiful fonts that miss "Ç" or "~" and "^" =/ So I can't use them for the portuguese version ><
I usually add more space between letters and lines, I try to make it easy for me to read, at least.
For onomatopoeia I usually go for Comic Book Commando.
Here is a page of Delphinium, with Candara, Comic Book and Comic Book Commando: