There are several areas on the pitch where we need reinforcements, but some of these wouldn't need spending transfer funds on, but let's discuss all of them:
1) A winger. Left, right, left-footed, right-footed, no difference. Of our all wingers only Mirallas has enough quality to feature regurarly. McGeady is crap more often than not, Atsu isn't of Premier League (yet?), Barkley, Osman are no wingers, Pienaar is on the wrong side of 30 and scores less goals than some of Europe's centre-backs. We could do really worse than loaning Joel Campbell from Arsenal, or buying Red Bull Salzburg's Kevin Kampl. We could also permanently move Bryan Oviedo further up the pitch, as Garbutt has shown that he can be a great deputy for Leighton Baines right now, thus three good left-backs is one to many.
2) Should Barkley play deeper (as was the case v. QPR; I really hope it stays this way) on a regular basis, we need someone to bring a creative spark into the midfield, a more typical "10", if you will. I believe Alexandru Maxim from VfB Stuttgart would fill that role perfectly. Other interesting, yet relatively cheap prospects could be: Barcelona's Rafinha, Chelsea's Thorgan Hazard (on loan to Borussia Mönchengladbach) or even Olympique Lyon's Clément Grenier (although plagued by injuries, thus I'd focus on the former three).
3) A quality second-stringer for a right-back spot. Browning has shown he has what it takes in several cameos this season, thus I'd give him some playing time should Séamus Coleman be unavailable.
4) A goalkeeper. Let's be honest, Howard won't be any younger regardless of any miraculous diet or tricks he tends to use. The older a footballer gets, the more mistake-prone he is and our own Captain America is a perfect example of that. Joel isn't of quality Everton require, he should be sold immediately. Germany is the market I'd take a look at in this department, as the German Bundesliga has a lot of talented and at the same time experienced goalies. Kevin Trapp, Ron-Robert Zieler are already very good (especially the first one) and both can be pretty cheap come summer, as both see their contracts expire in June 2016. But in the current situation, I'd take an especially long look at FSV Mainz 05's Loris Karius, who is available on a Bosman in June 2015. Considering that, he would be really cheap in January, but would instantaneously add much needed quality to our goal.
5) A centre-back. Both Alcaraz and Distin see their contracts end in June 2015. Barry was given 3-year contract extension and I believe he could add depth to that position, as Bešić, McCarthy, Barkley all played better than our midfield veteran this term. But with Stones, Jagielka and Barry we'd still need a fourth centre-back. Aston Villa's Winston Reid is already proven in the Premier League and sees his contract expire in June 2015. I know there will be competition to sign him but I believe we should do as much as we can to get him. If not, other interesting (and free!) options include: FC Basel's Fabian Schär or Eintracht Frankfurt's Carlos Zambrano.