Naturally, of course, I'd like to see bigger donations.
But my usual answer is; whatever you feel the artwork is worth to you. Plenty of people only donate a dollar, the occasional few give $20 or so. The rare patron has given $50, or even more.
If I may, I would suggest a donation of around $5 or $10. More, if you can spare it or enjoy the artwork. These wallpapers take time- I probably have about eight in this one, not counting what it took to update the page.
Yeah, I realize that even for expert artists (which you have in the past said you're not, as I recall) images don't just magically materialize on paper or the screen.
My problem is that what I think a work is worth in monetary terms tends to exceed what spare cash is available. Someone needs to invent shorter months so I have more money at the end of them, dammit. :P
In any case, I'll be throwing some bucks your way in a minute.