Here we have the rather interesting DVD sales ranking for 2008 anime, in this case focused on the first volume as a proxy for total popularity. There are a number of interesting results within the list, but the top and bottom are likely not surprising.
These numbers are the number of DVDs sold over the period specified. All titles mentioned are the first volume unless otherwise stated:
39,251 コードギアスR2 / Code Geass R2 (7 weeks)
27,142 マクロスF / Macross F (6 weeks)
14,520 ARIA The ORIGINATION (1 month)
11,944~ ストライクウィッチーズ 限定版 / Strike Witches LE (3 weeks)
11,712 図書館戦争 / Toshokan Sensou (4 weeks)
11,531 純情ロマンチカ 限定版 / Junjou Romantica LE (1 month)
11,006 墓場鬼太郎 / Hakaba Kitarou (1 month)
10,367 To LOVEるドキ×2エディション / To Love-Ru (1 month)
9,823 ソウルイーター / Soul Eater (1 month)
9,689 ひだまりスケッチ×365 (限定版) / Hidamari Sketch×365 LE
9,327 かのこん 限定版 / Kanokon LE (4 weeks)
9,139~ 狼と香辛料 / Spice and Wolf (1 month)
8,532 一騎当千 Great Guardians 第壱巻 / Ikki Tousen 2 (2 weeks)
7,444~ ロザリオとバンパイア / Rosario + Vampire (1 month)
7,161 乃木坂春香の秘密 〈限定版〉 / Nogizaka Haruka no Himitsu LE
5,937 ゼロの使い魔～三美姫の輪舞～ / Zero no Tsukaima III (2 weeks)
5,251 俗・絶望先生 / Zoku Sayonara Zetsubou Sensei (First week)
5,128 みなみけ～おかわり～ / Minamike Okawari (2 weeks)
4,981 恋姫†無双 生産限定特装版 / Koihime Musou LE
4,864 xxxHOLiC◆継 / xxxHOLiC (First week)
4,830 PERSONA -trinity soul- (First week)
3,926 D.C.II S.S. (限定版) / Da Capo Season 2 LE (First week)
3,773 ドルアーガの塔 / The Tower of Druaga (2 weeks)
3,278 チーズスイートホーム〈限定版〉 / Chi’s Sweet Home LE (First week)
3,214 スレイヤーズREVOLUTION / Slayers Revolution (First week)
3,040 仮面のメイドガイ 〈限定版〉/ Kamen no Maid Guy LE (First week)
2,869 true tears (First week)
The top slots won’t surprise anyone, and for that matter nor will the bottom (Kamen no Maid Guy), although Slayers fans will depressed by the doom such results spell for future Slayers titles.
There are a few non-mainstream anime in there, such as yaoi anime Junou, or the various children’s anime such as Kanokon and GeGeGe no Kitarou, but it seems the vast majority are in conformance with ratings and critical reception.
The fact that some titles only have a few weeks to accumulate sales is significant, but it should be noted that most titles see the vast majority of their sales in the first week, so this is not a huge factor.