You could work more on donation drives. Maybe set up a sort of fun-raiser, have people willing to donate.
A really good system to use is have a level of degree for donators.
The system my clan uses is this:
Donations are not reset, once you have donated those donations are added to your tally for life.
$5+ = Get a donator rank, get two permissions on the TF2 server, get your name mentioned on the front page and in a sticky post.
$20+ = Get a donator+ Rank, get six permissions on the TF2 server and some permissions on Gmod.
$50+ = Get sponsor rank, get 10 permissions on TF2 server and more on Gmod.
I realize you don't have game servers, so the permissions will have to work a different way, but having different ranks for different donators depending on how much they pay can be a good incentive.
Also, when someone donates and you do get a sizable donation, publicly thanking the donators can make other people feel more inclined to donate so they get thanked as well. Having a sticky thread of all the people who have donated and how much they've donated (ranked most being on top) can also be very helpful.
I also think being more public about the raffle would be a good idea. Maybe put something about it on the front page? Another thing is, if you are actually in financial trouble, doing a public post that you need donations, although is a bit iffy (as in yes, it does make you feel bad) but it will get you a few donations.
My clan does it and we've made over $450 in the last 3 months, purely in donations.
Also an idea we will be implementing to the clan soon is forum achievements, you get achievements for posting x amount, going to x boards, being online x amount of times, posting secret messages and donating
. We haven't implemented it (or made it yet, we're going to use an original program made by our web development team) but it should be good, increase activity and donations for those who want all the achievements.