Nobody has mentioned his backing in the People for Ethnic Treatment of Animals-concert around 1999-2000.
Playing with has beens (the bassplayer from Beatles, the drummer from Deep Purple, pianoman from Everly Bros and guitarplayer from B.j.K and the Dakotas) the set was excerpts from "Live at the Cavern" i.e. parts from "Run Devil Run"...
I love his playing at the 2004 Strat Pack gig. I watched the whole gig at some point and it was ok but hardly that amazing. There is some ok jamming and such but it is a bit restrained and distant. However Gilmour comes out and plays with that depth and quality of sound and it changes everything. I feel he showed everybody up at that gig quite well. Everybody seems a little rusty and half-assed until Gilmour turns up.
For me, the best are: 1) Dream Academy's "It'll Never Happen Again," a cover of the great Tim Hardin song (Gilmour's presence makes this a great neo-Floyd song in the same way that, say, "No Way Out of Here" is); 2) "You" by Roy Harper - which sounds like it belongs on THE WALL and would've been a highlight on the album.
After that, other songs might be really cool (say, for example, Kate Bush's "Pull Out the Pin"), but they belong to those artists more than they belong to the Gilmour/Floyd oeuvre. IMHO.