Justin,
It's very cool for your brother to be marrying a woman whom you sincerely appreciate.
A couple of thoughts.... First, whatever you end up, from the heart, with will be great.
Lots of wedding toasts begin with humor. Something like: Marriage is a wonderful institution and I wish you well living the rest of your lives in an institution.
Also, you may want to first briefly address your brother, then his bride, then a blessing or wishing well for them as a couple.
googling wedding toast yields gobs of toasts. It could be worth reading through some of those to see if there are any phrases or ideas that ring true for your expression of caring.
I second the idea that it's o.k. to have the toast written for reference. It indicates caring enough to get the words right.
"I know I'm paranoid.... but, am I paranoid enough?" --Tom Clancy